Temperature-controlled purge gate valve for chemical vapor deposition chamber

ABSTRACT

The present invention relates to methods and apparatus that are optimized for producing Group III-N (nitrogen) compound semiconductor wafers and specifically for producing GaN wafers. Specifically, the methods relate to substantially preventing the formation of unwanted materials on an isolation valve fixture within a chemical vapor deposition (CVD) reactor. In particular, the invention provides apparatus and methods for limiting deposition/condensation of GaCl 3  and reaction by-products on an isolation valve that is used in the system and method for forming a monocrystalline Group III-V semiconductor material by reacting an amount of a gaseous Group III precursor as one reactant with an amount of a gaseous Group V component as another reactant in a reaction chamber.

FIELD OF THE INVENTION

The invention disclosed herein comprises methods for substantiallypreventing the formation of unwanted materials on an isolation valvefixture within a chemical vapor deposition (CVD) reactor. In a preferredembodiment, the invention provides apparatus and methods for limitingdeposition/condensation of GaCl₃ and reaction by-products on anisolation valve.

BACKGROUND OF THE INVENTION

Group III-V compounds are important semiconductor materials useful forfabricating optic components (particularly, short wavelength LEDs andlasers) and electronic components (particularly,high-temperature/high-power transistors). However, the commercialexploitation of these III-V compounds has been hindered by the practicalimpossibility of directly growing bulk single crystal substrates ofthese substances. As most of these materials are therefore manufacturedby heteroepitaxial CVD processes, their commercial exploitation has alsobeen hindered by lack of practical epitaxial substrates for growth oflow-defect density, monocrystalline layers of III-V compounds.

In the case of III-nitrides, one state-of-the-art approach to improvingthe quality of heteroepitaxially-grown material is to grow very thicklayers. It has been discovered that, even though the lower portions of athick layer may have excessive defect densities, the upper portions cannevertheless have adequate defect densities. However, growth of thicklayers requires growth rates currently achievable only with hydride(halide) vapor phase expitaxy (HVPE). HVPE processes are conducted inCVD reactors, use precursor gases including corrosive chlorinecompounds, and are conducted with a substrate at significantly elevatedinternal temperatures so as to promote a desired reaction between theprecursor gases.

However, not all internal reactor components need be maintained at thehigh reaction/deposition temperatures, nor is it desirable to do so. Forexample, the walls of the CVD reactor chamber can be maintained at lowertemperatures in order to limit unwanted deposition of target material onthe reactor walls. Also, certain components within the reactor, e.g.,o-rings, seals, gaskets, and the like, should be maintained at lowertemperatures because they are often made of polymeric materials whichcan be damaged by higher temperatures.

On the other hand, it is also not desirable for internal components tobe at too low a temperature. For example, precursor gases or reactionproducts can condense on internal components at lower temperatures.Also, internal components at lower temperatures can cause undesirableinteractions, such as complex formation, between the gases present inthe reactor. Such effects can damage internal components and causecontamination of a growing semiconductor wafer.

Certain components can be both exposed to the interior of a reactorchamber and include temperature-sensitive materials, e.g., polymericseals, and such components can be subject to the conflictingrequirements, being at both higher and lower temperatures. Examples ofsuch components (with conflicting temperature requirements) present inmany commercial CVD reactors are gate valves (or load locks or transferdoors, or the like). Such commercial reactors often feature automatedtransfer of wafers between the interior of the reactor chamber and anintermediate environment known as a transfer chamber (or load chamber ortransfer chamber, or the like). Such automated transfer means usuallyinclude an automated gate valve which, when open, accommodate wafertransfer and the automated wafer transfer devices, and which, whenclosed, seal the interior of the chamber from the exterior.

Briefly, when closed, at least a face of a gate valve is exposed to thereactor-chamber interior, and the temperature of the exposed face shouldbe high enough so that described undesirable condensation/reaction islimited. Also, when closed, the face of a gate valve should form a sealwith an external face of the reactor, and the temperature in thevicinity of this must be low enough so that damage to sealing materials,e.g., gaskets, o-rings, and the like, is limited. Preferably, anythermal damage to the sealing materials is sufficiently low so that thegate valve can be opened and closed many thousands times without repair.

In the particular case of HVPE growth of GaN, a gate valve (or theisolation valve) assembly can be exposed to process gases includingGaCl₃, NH₃, HCl, N₂, H₂ and Ar and to reaction products and by-productsincluding NH₄Cl. Of these, the more problematic are the precursor gasGaCl₃ and the reaction product NH₄Cl. GaCl₃ is corrosive and cancondense on surfaces below ≈80° C. NH₄Cl can condense on any surfaceinside the reaction chamber which is less than 150° C. Further, only alimited number of sealing materials are sufficiently resistant tocorrosive chlorine-containing gases, and these generally cannotwithstand temperatures in excess of ≈150-160° C.

The prior art describes methods purporting to protect reactor componentsfrom corrosive materials and to prevent condensation on cooler reactorcomponents. For example, U.S. Pat. No. 6,071,375 teaches protecting aninternal component in a reactor by arranging it in a recessedpre-chamber that is open to the reactor but kept relatively free ofprocess gases by an inert purge gas stream injected into thepre-chamber. However, such arrangements involving pre-chambers would becumbersome for high volume manufacturing equipment which generally hasstringent size limitations. Also, U.S. Pat. No. 6,086,673 teaches a twozone, hot-wall reactor. In a precursor production zone, the temperatureis of the order of 850° C., whilst in a growth zone, the temperature isof the order of 1050° C. However, hot wall reactors are inappropriatefor high volume manufacturing processes because nitride deposition onthe hot walls necessitates frequent chamber cleaning. Also, the problemof sealing an automated gate valve is not addressed here. U.S. Pat. No.5,156,521 illustrates an exemplary prior art gate valve.

The prior art is lacking in sealing methods and gate valve apparatus fora CVD chamber suitable for use in high volume manufacture ofsemiconductor materials, especially high volume manufacture ofIII-nitride and GaN materials.

SUMMARY OF THE INVENTION

The invention relates to a method for forming a monocrystalline GroupIII-V semiconductor material, by reacting an amount of a gaseous GroupIII precursor as one reactant with an amount of a gaseous Group Vcomponent as another reactant in a reaction chamber under conditionssufficient to manufacture the semiconductor material, and introducingthe reactants so that they react at a predetermined location in thereaction chamber while injecting one or more purge gas streams to assistin directing at least one of the reactants to the predeterminedlocation. The gaseous Group III precursor is continuously provided at amass flow of at least 50 g Group III element/hour for a time of at least48 hours.

The Group III precursor and Group V component are introduced into thereaction chamber in a controlled manner to react at the predeterminedlocation adjacent and above one or more substrates to deposit themonocrystalline semiconductor material thereon. The reaction chamber isgenerally configured as a horizontal rectangular chamber and the methodfurther comprises introducing the reactants through different portionsof the chamber to avoid reacting until they reach the predeterminedlocation adjacent and above the substrate(s).

More particularly, the reaction chamber may include a floor, a ceiling,a pair of sidewalls, an open inlet and an open outlet, and the methodfurther comprises introducing one reactant through the floor of thechamber while introducing the other reactant through the inlet incombination with the one or more purge gas streams, to direct the otherreactant to the predetermined location to efficiently deposit themonocrystalline material on the substrate(s). When one reactant may beintroduced through a slot in the floor of the chamber, the otherreactant may be introduced at or near the inlet and which furthercomprises providing a gate valve in the reaction chamber inlet throughwhich the purge gas stream(s) pass to enter the chamber and at leastdirect the other reactant to the predetermined location. The reactantthat is introduced through the floor of the chamber is preferably thegaseous Group III precursor and the other reactant that is introducedthrough the inlet is preferably the Group V component, with a pluralityof the purge gas streams provided to assist in directing the Group IIIprecursor to the predetermined location.

The reaction chamber is generally made of quartz, and the gate valve ismade of metal, so that the method further comprises providing an O-ringbetween the gate valve and reactor, and cooling the gate valve to avoiddeteriorating the O-ring during operation. Also, the reactants arepreferably provided as horizontal laminar flows in the reaction chamberand the plurality of gas streams introduced through separate aperturesin the gate valve. For this, the apertures are advantageously providedin spaced relation in a face of the gate valve with the spacing betweenthe apertures in a central portion of the face being greater than thespacing in other portions of the face.

When the gaseous Group V component is a nitrogen containing component,it is provided in a substantially greater amount than that of thegaseous Group III precursor so that a monocrystalline Group III nitrideis provided. The Group III precursor may be gallium, aluminum or indiumand the nitrogen containing component is a nitrogen containing gas suchas ammonia or a nitrogen ion or radical generated by plasma-activationof nitrogen gas.

The invention also relates to a system for manufacture of amonocrystalline Group III-V semiconductor material. This system includesa source of a Group III precursor for use as one reactant, a source ofGroup V component for use as another reactant, a reaction chamber thatreceives the Group III precursor and Group V component for reactiontherewith under conditions sufficient to form the monocrystalline GroupIII-V semiconductor material, and apertures for introducing thereactants into the reaction chamber so that they meet and react at apredetermined location and for injecting one or more purge gas streamsinto the reaction chamber to assist in directing at least one of thereactants to the predetermined location.

The reaction chamber is generally configured as a horizontal,rectangular chamber and the apertures for introducing the reactants arelocated in different portions of the chamber to avoid reaction untilthey meet at a predetermined location adjacent and immediately above thesubstrate(s). Also, as noted above, the reaction chamber includes afloor, a ceiling, a pair of sidewalls, an open inlet, an open outlet,and one reactant entry aperture comprises a horizontal slot in the floorfor introducing that reactant into the reaction chamber, with the slotconfigured and dimensioned to introduce the reactant and to direct it tothe predetermined location for reaction with another reactant.

The system further comprises a rotatable support for holding one or moresubstrates upon which the monocrystalline semiconductor material is tobe deposited, and the apertures allow introduction of the reactants intothe reaction chamber in a controlled manner with the substrates andsupport configured, dimensioned and positioned with respect to thereactant entry apertures to facilitate formation and deposition of themonocrystalline semiconductor material upon the substrate(s). The entryaperture for the other reactant comprises an injection nozzle and atleast one other aperture comprises a passage for introducing the one ormore purge gas streams into the reaction chamber to direct the otherreactant to the predetermined location to efficiently form themonocrystalline material on the substrate(s).

In a preferred embodiment, a gate valve associated with the inlet isprovided for introducing the purge gas stream(s) in a manner thatdirects the other reactant to the predetermined location to efficientlyform the monocrystalline material upon the substrate(s). The reactantthat is introduced through the floor of the chamber is preferably thegaseous Group III precursor and the other reactant that is introducedthrough the inlet is preferably the Group V component, with the gatevalve including a plurality of the apertures for introducing the purgegas streams into the reaction chamber to assist in directing the GroupIII precursor to the predetermined location.

The system typically provides the reactants to enter the reactionchamber as horizontal laminar flows with the plurality of purge gasstreams enter through separate apertures in the gate valve. This can beachieved by providing apertures in spaced relation in a face of the gatevalve with the spacing between the apertures in a central portion of theface being greater than the spacing in other portions of the face. Whenthe reaction chamber is made of quartz and the gate valve is made ofmetal, an O-ring located between the gate valve and reactor may beincluded for providing a sealing connection. Also, the gate valve may becooled by the purge gas stream(s) to avoid deteriorating the O-ringduring operation.

The invention also relates to a method for forming a monocrystallineGroup III-V semiconductor material by reacting an amount of a gaseousGroup III precursor as one reactant with an amount of a gaseous Group Vcomponent as another reactant in a reaction chamber under conditionssufficient to manufacture the semiconductor material, where thereactants are introduced into the reaction chamber so that they react ata predetermined location in the reaction chamber adjacent and above oneor more substrates to deposit semiconductor material thereon and alsoinjecting one or more purge gas streams to assist in directing at leastone of the reactants to the predetermined location. Especially, thismethod continuously provides the gaseous Group III precursor at a massflow of at least 50 g Group III element/hour for a time of at least 48hours.

More particularly, the invention injects the purge gas streams through aplurality of apertures in a gate valve that is closable to seal an inletport of the reaction chamber and openable to allow transfer of materialsbetween the reaction chamber interior and exterior through the inletport. Portions of the gate valve adjacent to a seal between the gatevalve when closed and the reaction chamber can be sufficiently cooled inorder to avoid thermal deterioration of the seal during operation, e.g.,cooled by passing cool fluids through passages that areconductively-coupled to the gate valve. Additionally, portions of thegate valve exposed to the reaction chamber interior when closed can besufficiently heated in order to avoid condensation of and/or unwantedreaction between gases in the reactor while limiting the heating so asto avoid thermal deterioration of a seal between the gate valve whenclosed and the reaction chamber. The gate valve can be heated by passinga heated fluid through one or more passageways internal to the gatevalve. Exemplary temperatures are greater than either or both of acondensation temperature of the Group III precursor and a sublimationtemperature of a product of a Group III-Group V reaction.

The invention also relates to a gate valve assembly useful in a CVDreaction chamber, the assembly that is closable to seal a materialtransfer port into the reaction chamber and openable to allow transferof materials through this transfer port which includes temperaturecontrol that maintains gate valve temperatures in selected ranges duringreaction-chamber operation.

More particularly, the temperature control can include one or moreheating elements, such as radiant-heating elements external to the gatevalve or passages internal to the gate valve for heated fluids, forsufficiently heating the portions of the gate valve exposed to thereaction chamber interior when closed in order to avoid condensation ofand/or unwanted reaction between gases in the reactor. When the gatevalve assembly includes a seal between the closed gate valve and thereaction chamber, the temperature control preferably also includesfurther one or more cooling elements, such as one or more passages forcooled fluids that are conductively-coupled to the gate valve, forsufficiently cooling portions of the gate valve adjacent to the seal toavoid thermal deterioration of the seal during operation.

The gate valve also preferably provides a plurality of aperturesconfigure to inject gas streams into the reaction chamber duringoperation. These apertures can either be in a spaced relation with thespacing between the apertures in a central portion being greater thanthe spacing of the apertures in other portions or in a spaced relationwith the substantially uniform spacing between the apertures.

The invention also relates to a system for manufacture of amonocrystalline Group III-V semiconductor material. A system of thisinvention includes a source of a Group III precursor for use as onereactant, a source of Group V component for use as another reactant, anda reaction chamber that receives the Group III precursor and Group Vcomponent for reaction therewith under conditions sufficient to form theGroup III-V semiconductor material. The reaction chamber preferably hasapertures for introducing the reactants into the reaction chamber sothat they meet and react at a predetermined location in the reactionchamber adjacent and above one or more substrates to depositsemiconductor material thereon, apertures for injecting one or morepurge gas streams, and a loading port through which semiconductormaterials can be transferred between the interior and exterior of thereactor. The system also preferably has a gate valve assembly that sealsthe loading port with a seal between the gate valve and reactor andincludes a temperature control for controlling the temperature of thegate valve so as to avoid both condensation of and/or unwanted reactionbetween gases in the reactor and also thermal deterioration of the seal.

The gate valve of the system preferably provides a plurality ofapertures through which the purge gas streams are injected into thereaction chamber in a manner that at least partially directs onereactant to the predetermined location. And the temperature controlpreferably has one or more heating elements for sufficiently heatingportions of the gate valve exposed to the reaction chamber interior whenclosed in order to avoid condensation of and/or unwanted reactionbetween gases in the reactor. The temperature control preferably has oneor more cooling elements for sufficiently cooling portions of the gatevalve adjacent to the to avoid thermal deterioration of the seal duringoperation, and one or more elements for sensing temperatures of the gatevalve and for providing feedback to the temperature control.

The reaction chamber is configured arranged so that the reactants enterthe reaction chamber as horizontal laminar flows. It is optionallyfurther configured with a floor, a ceiling, a pair of sidewalls, an openinlet, an open outlet, and one of the reactant entry apertures is ahorizontal slot in the floor for introducing that reactant into thereaction chamber, with the slot configured and dimensioned to introducethe reactant and to direct it to the predetermined location for reactionwith another reactant.

Further aspects and details and alternate combinations of the elementsof this invention will be apparent from the appended drawings andfollowing detailed description and these are also within the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be understood more fully by reference to thefollowing detailed description of the preferred embodiment of thepresent invention, illustrative examples of specific embodiments of theinvention and the appended figures in which:

FIG. 1 illustrates schematically systems of the invention;

FIGS. 2A-C illustrates preferred GaCl₃ sources;

FIGS. 3A-C illustrates preferred reaction chambers;

FIG. 4 schematically preferred transfer/reaction chamber combinations;

FIG. 5 schematically illustrates preferred inlet manifold structures;

FIG. 6 illustrates schematically an alternative reactant gas inletarrangement;

FIG. 7A-B illustrate preferred embodiments of gate valves; and

FIG. 8A-C illustrate further preferred embodiments of gate valves.

The same reference numbers are used to identify the same structuresappearing on different figures.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention provides equipment and methods for high growth rate andhigh volume manufacturing of Group III-V compound semiconductor wafersnot hitherto possible. The equipment is capable of sustained productionin that over periods of weeks or months production does not need to beshut down for maintenance. The equipment is capable of high-throughputproduction in that at least a wafer (or a batch of wafers) can beproduced every one to four hours. The Group III-V compound semiconductorwafers so produced are suitable for fabrication of optical andelectronic components, for substrates for further epitaxial depositionand for other semiconductor material applications.

In preferred embodiments, the equipment and methods are specificallydirected to producing GaN nitride wafers, and such embodiments are thefocus of much of the subsequent description. This focus is for brevityonly and should not to be taken as limiting the invention. It will beappreciated that the preferred embodiments can readily be adapted toproducing wafers of other Group III nitrides, e.g., aluminum nitride,indium nitride, and mixed aluminum/gallium/indium nitrides, and toproducing wafers of Group III phosphides and arsenides. Accordingly,producing semiconductors wafers or wafers of any of the III-V compoundsemiconductors are within the scope of this invention.

This invention can be particularly cost effective because particularembodiments can be realized by modifying equipment already commerciallyavailable for epitaxial deposition of Si. Thereby, focus can be on theelements and features that are especially important to GaN epitaxy whileaspects related to high volume manufacturing, which are well developedin silicon technology, can be maintained. Also, the equipment of thisinvention is designed to have a significant duty cycle so that it iscapable of high volume manufacturing. Also, the invention provides forvirtually 100% efficiency in the use of expensive Ga by recovering andrecycling of Ga that is not actually deposited and is thereforeexhausted from the reaction chamber equipment; with limited downtimeneeded. Also, the inventive process and apparatus include an economicaluse of Ga precursors.

The invention includes the use of a known low thermal mass susceptor(substrate holder) and lamp heating with temperature controlled reactorwalls. The use of lamp heating permits the heat energy to mainly becoupled to the susceptor and not heat the reactor walls. The lampheating system is equipped with a control system to permit very fastpower changes to the lamps. The low thermal mass susceptor coupled withthe lamp heating system permit very fast temperature changes, both upand down. Temperature ramp rates are in the range of 2-10 degrees/secondand preferably on the order of 4-7 degrees/second.

The invention includes reactor walls that are controlled to a specifictemperature to minimize undesired gas phase reactions and preventdeposition on the walls. The lack of wall deposition permitsstraightforward use of in-situ monitoring for growth rate, stress andother pertinent growth parameters.

The invention includes one or more external sources for the Group IIIprecursor(s). The flow of the Group III precursor is directly controlledby an electronic mass flow controller. There is no practical limit onthe size of the external Group III source. Group III source containerscan be in the range of 50 to 100 to 300 kg, and several sourcecontainers could be manifolded together to permit switching betweencontainers with no down time. For the deposition of GaN, the Gaprecursor is GaCl₃. This Ga source is based on the observations anddiscoveries that, when GaCl₃ is in a sufficiently low viscosity state,routine physical means, e.g., bubbling a carrier gas through liquidGaCl₃, can provide a sufficient evaporation rate of GaCl₃, and thatGaCl₃ assumes such a sufficiently low viscosity state in a preferredtemperatures of range of 100 to 130° C.

The invention includes equipment for maintaining the GaCl₃ at a constanttemperature and pressure in the low viscosity state and equipment forflowing a controlled amount of gas through the liquid GaCl₃ anddelivering the GaCl₃ vapor to the reactor. This equipment can sustainhigh mass flows of GaCl₃ (in the range of 200 to 400 g/hour) that resultin GaN deposition rates in the range of 100 to 400 μm/hour on one 200 mmdiameter substrates or any number of smaller wafers that fit on thesusceptor. The delivery system from the GaCl₃ container is maintainedwith a specific temperature profile to prevent condensation of theGaCl₃.

The invention also includes an inlet manifold structure that keeps theGroup III and Group V gases separate until the deposition zone and alsoprovides a method for achieving high gas phase homogeneity in thedeposition zone, thus achieving a uniform flow of process gases into thereaction chamber and across the susceptor supporting the substrates. Theprocess gas flow is designed to be substantially uniform in both flowvelocity (therefore, non-turbulent) and chemical composition (therefore,a uniform III/V ratio). In a preferred embodiment, this is realized byproviding separate primary inlet ports for the Group III and Group Vgases that provide uniform distribution of gas across the width of thereactor, and to achieve high uniformity. In preferred embodiments, themanifold and port structures are designed and refined by modeling gasflows according to principles of fluid dynamics.

The invention also includes a method to add energy to either or both theGroup III or Group V inlets to enhance the reaction efficiency of theseprecursors. In a preferred embodiment, this would include a method forthermal decomposition of the dimer form of the Group III precursorGa₂Cl₆ into the monomer GaCl₃. In another preferred embodiment, thiswould include a method for decomposition of the ammonia precursor, forexample by thermal decomposition or plasma.

The invention also includes equipment for automated wafer handling,including fully automatic cassette-to-cassette loading, separate coolingstages, load locks, non-contact wafer handlers, all of which are fullycomputer controlled and interfaced to the overall growth program.

The invention also includes temperature control of the reactor inlet andoutlet flanges and the exhaust system and a specially designed pressureregulating valve that can operate at reduced pressure and hightemperatures. Temperature control in these areas prevents premature gasphase reactions and minimizes deposits of GaN as well as variousreaction byproducts. A major reaction byproduct is NH₄Cl. Thetemperature of the entire exhaust downstream of the reactor iscontrolled to prevent condensation of NH₄Cl.

The invention also includes a gate valve that opens to allow transfer ofwafers between the interior of the reactor chamber and the exterior, andthat closes to seal the interior of the reactor chamber from theexterior. The gate valve preferably includes a plurality of inlet ports,which, in preferred embodiments, are used to admit inert gases tocontrol and reduce deposits on the valve material and the side walls ofthe reactor and to reduce gas recirculation and reduce residence time ofthe gases in the reactor. Preferably, at least the sealing face of thegate valve is temperature controlled.

Additional aspects and details of the invention include the use of asusceptor that can hold one or more wafers during one growth run and asusceptor designed to prevent attachment of the substrate to thesusceptor during thick growth runs.

The present invention is based on the discovery that specific metalhalide compounds have certain unique chemical properties, and that whencoupled with an apparatus designed in light of these properties, thecombination can be used to deposit thick layers of Group III-V compoundsemiconductors, and in particular gallium nitride, with heretoforeunachievable high throughput, high uptime and low cost in a mannercharacteristic of high volume manufacturing.

For this invention, “high volume manufacturing” (or HVM) ischaracterized by high throughput, high precursor efficiency and highequipment utilization. Throughput means the number of wafers/hour thatcan be processed. Precursor efficiency means that a large fraction ofthe material input to the system goes into the product and is notwasted. Although there are a large number of variables associated withthe material, process and structure, HVM deposition rates range fromaround 50 g Group III element (such as gallium) per hour for a period ofat least 48 hours, to 100 g Group III element per hour for a period ofat least 100 hours, to 200 g Group III element per hour for a period ofat least one week, to as much as 300 to 400 g Group III element per hourfor a period of at least a month. A typical source capacity can rangefrom 5 Kg to 60 Kg in one vessel and for increased HVM, multiple vesselscan be operated in series. This can provide Group III-V materialthroughputs that are similar to those obtained in silicon manufacture.

Equipment utilization means the ratio of the time that the substrate isin the reactor compared to a given time period, such as 24 hours. ForHVM, most of the time is spent producing product as opposed to set-up,calibration, cleaning or maintenance. Quantitative ranges for thesemeasures are available for mature silicon semiconductor processingtechnology. The equipment utilization for HVM of Group III-V material ison the order of about 75 to 85%, which is similar to that of siliconepitaxial deposition equipment.

Reactor utilization is the period of time during which growth of thematerial on the substrate is occurring in the reactor. For conventionalHVPE reactors, this value is on the order of 40 to 45%, while for a HVMreactor such as those disclosed herein, this value is on the order of 65to 70%.

Growth utilization is the overhead time in the reactor, meaning that itis the time during which growth is occurring in the reactor after asubstrate is provided therein. For conventional HVPE reactors, thisvalue is on the order of 65 to 70%, while for a HVM reactor such asthose disclosed herein, this value is on the order of 95% to close to100%, i.e., close to that of a silicon manufacturing process.

The present invention addresses the main limitations of the current HVPEtechnology which prevent high volume manufacturing. This is done byreplacing the current HVPE in-situ source generation with an externalsource and replacing the current HVPE high thermal mass hot wall reactorwith a low thermal mass reactor with temperature controlled walls. Theuse of an external source eliminates the need to stop production tocharge the precursors, greatly increasing the equipment utilization.Furthermore, the mass flux of the precursor is controlled directly by anelectronic mass flow controller, resulting in improved control of thegrowth process and improve yield. The low thermal mass reactor withtemperature controlled walls greatly reduces the time required forheating and cooling, both during growth and maintenance. The ability torapidly heat and cool the substrate also permits the use ofmulti-temperature processes, which are not practically possible in thecurrent HVPE hot wall system. The ability to control the walltemperature reduces gas phase reactions and almost completely eliminateswall deposits. Elimination of wall deposits greatly increases the timebetween cleaning, leading to high reactor utilization.

The present invention is based on the fact that certain metal halidecompounds can be used as an external source for HVPE deposition of III-Vcompound semiconductors and can provide, in conjunction with specificdelivery equipment detailed in this invention, a sufficiently high massflux to achieve and maintain high deposition rates on large areas. Inparticular, when melted, GaCl₃ is in a sufficiently low viscosity stateto permit routine physical means, e.g. bubbling with a carrier gasthrough liquid GaCl₃, can provide a sufficient evaporation rate ofGaCl₃, and that GaCl₃ assumes such a sufficiently low viscosity state attemperatures in a range about approximately 130° C. Furthermore thisinvention is based on the fact that GaCl₃, in the liquid phase and inthe gas phase at temperatures below about 400° C. is actually a dimer.The chemical formula for the dimer can be written either as (GaCl₃)₂ orGa₂Cl₆.

In addition to Ga₂Cl₆ related chlorogallanes can also be used as a Gaprecursor. These compounds are similar to Ga₂Cl₆ but with H replacingone or more Cl atoms. For example monochlorogallane has the two bridgeCl atoms replace by H atoms. As shown below, the terminal Ga-bondedatoms can also be replaced by H (note that there is a cis and transversion of this compound). According to B. J. Duke et al, Inorg. Chem.30 (1991) 4225, the stability of the dimer decreases with increasingchlorination of the terminal Ga-x bonds by 1-2 kcal/mol per Clsubstitution and increases by 6-8 kcal/mol with each Cl substitution fora bridging H atom. Thus as the number of substituted Cl atoms decreases,the fraction of the monomer, at a given temperature, would decrease.

The growth of In- and Al-containing compounds can be achieved usingsubstantially similar equipment but with the limitation that thesesources are not as easily kept in a liquid state. InCl₃ melts at 583° C.While the present invention described for GaCl₃ may be modified tooperate at temperatures above 583° C., this is practically quitedifficult. An alternate approach is to heat the InCl₃ to a temperaturebelow the melting point but where the vapor pressure is sufficient toachieve acceptable deposition rates.

AlCl₃ sublimes at 178° C. and melts at 190° C. and 2.5 atm. The presentinvention described for GaCl₃ can be modified to operate at higher thanatmospheric pressure and temperatures above the melting point of AlCl₃.Additionally, the alternate approach described above for InCl₃, heatingbelow the melting point to achieve a sufficiently high vapor pressure,will also work. AlCl₃ also forms a dimer (AlCl₃)₂ in the liquid phaseand in the gas phase at low temperatures.

Another main component of this invention is a low thermal mass reactor.The low thermal mass reactor with temperature controlled walls greatlyreduces the time required for heating and cooling, both during growthand maintenance. The ability to rapidly heat and cool the substrate alsopermits the use of multi-temperature processes, which are notpractically possible in the current HVPE hot wall system. The ability tocontrol the wall temperature reduces gas phase reactions and almostcompletely eliminates wall deposits. Elimination of wall depositsgreatly increases the time between cleaning, leading to high reactorutilization.

The low thermal mass is achieved by using what is traditionally called acold wall system, but in this invention the wall temperature iscontrolled to a specific temperature. The current hot wall systems areheated by being enclosed in a furnace. In the new system, only thesubstrate holder and substrate are heated. There are many ways toachieve this including lamp heating, induction heating or resistanceheating. In one embodiment, the system consists of a reactor chamberconstructed from quartz and a substrate heater constructed of graphite.The graphite is heated by lamps on the outside of the quartz reactor.The quartz reactor walls can be controlled using a variety of methods.In most cases the wall temperature control system consists of one ormore methods to measure the wall temperature in a variety of locations,combined with a feedback system to adjust either cooling or heatinginput to the wall region to maintain the temperature at a preset value.In another embodiment, the wall temperature is controlled by fans thatblow air onto the exterior of the reactor walls for cooling. The walltemperature is not constrained to be constant at all times; thetemperature controller can be programmed to vary the temperature toachieve improved performance either during growth or maintenance.

Although the focus of the following description is primarily onpreferred embodiments for producing gallium nitride (GaN) wafers, itwill be appreciated that the equipment and methods described can bereadily adapted by one of average skill in the art to also producewafers of any of the III-V compound semiconductors are within the scopeof this invention. Accordingly, such equipment is within the scope ofthe invention. Headings are used throughout for clarity only and withoutintended limitation.

Also the invention provides equipment for high volume manufacturing ofGaN wafers that is economical to construct and operation. Preferredembodiments of the invention can be economically realized/constructed byadapting/modifying existing VPE equipment that has been designed for andis commercially available for silicon (Si) epitaxy. To practice thisinvention, it is not necessary to undertake an expensive and timeconsuming process of designing and constructing all components for GaNdeposition equipment from scratch. Instead, sustained, high-throughputGaN deposition equipment of the invention can be more rapidly andeconomically realized/constructed making targeted and limitedmodifications to existing Si processing production proven equipment.Along with such modified existing equipment, however, the invention alsoencompasses de novo construction.

Accordingly, the following description is first directed to thegenerally preferred features to be incorporated into existing Siequipment for GaN production. Features that can be retained from Siprocessing are not described in details as they are well known in theart. In different embodiments, different ones of the features to bedescribed can be implemented; the invention is not limited toembodiments implementing all these features. However, for higher levelsof sustained, high-throughout production, most or all of these featuresare advantageous and they include cassette to cassette loading, loadlocks and fully automated wafer handling with separate cooling stagewhich allows fast loading and unloading and processing a wafer while theother one is cooling. The loadlocks eliminate undesirable exposure ofthe reactor to atmosphere to minimize introduction of oxygen and watervapor and greatly reduce purge/bake time before running. Moreover theautomated handling reduces yield loss and wafer breakage from manualhandling of wafers. In some cases a Bernoulli wand is used to handle thewafers which allows hot loading and unloading at temperature as high as900° C. and save long cooling time.

General embodiments of the preferred features of this invention arefirst described in the context of a generic VPE system. It will becomeapparent how these general embodiments can be routinely adapted toparticular, commercially available, Si epitaxy equipment. The followingdescription is then directed to a particular preferred embodiment ofthis invention and of its preferred features that is based on one of theEPSILON® series of single-wafer epitaxial reactors available from ASMAmerica, Inc. (Phoenix, Ariz.). It is apparent, however, that theinvention is not limited to this particular preferred embodiment. Asanother example the inventions could easily be adapted to the CENTURA®series of AMAT (Santa Clara, Calif.).

Preferred embodiments of the equipment and methods of the invention (forproducing GaN wafers) are described in general with reference to FIG. 1.Particular preferred embodiments are then described in more detailedwith reference to FIGS. 2-5. Generally, the equipment of this inventionis designed and sized both for high volume manufacturing of epitaxialGaN layers on substrates and also for economy of construction andoperation.

GENERAL EMBODIMENTS OF THE INVENTION

For convenience and without limitation, the invention is generallydescribed with reference to FIG. 1 in terms of three basic subsystems:subsystems 1 for providing process gases (or liquids); subsystems 3including a reaction chamber; and subsystems 5 for waste abatement.

As noted above, HVM is an attribute of a combination of various physicalfeatures of the system including the generic features described herein:

1. External Source of GACL3

The structure of the first subsystem, the process gas subsystem,especially the gallium compound vapor source, is an important feature ofthe invention. Known GaN VPE processes are now briefly described. GaNVPE epitaxy comprises synthesizing GaN directly on the surface of aheated substrate from precursor gases containing nitrogen (N) andgallium (Ga) (and, optionally, one or more other Group III metalcontaining gases in order to form mixed nitrides and optionally, one ormore dopants to provide specific electronic conductivity). TheGa-containing gas is usually gallium monochloride (GaCl) or galliumtrichloride (GaCl₃), or a gallium-organic compound, e.g.,tri-ethyl-gallium (TEG) or tri-methyl-gallium (TMG). In the first case,the process is referred to as HVPE (Halide Vapor Pressure Epitaxy and inthe second as MOVPE (Metal Organic Vapor Pressure Epitaxy).

The chemical properties of GaCl (stability only at high temperatures)require that GaCl vapor be synthesized in situ in the reaction vessel,e.g., by passing HCl over a boat containing liquid Ga. In contrast,GaCl₃ is a stable solid at ambient conditions (in the absence ofmoisture) which is commonly supplied in sealed quartz ampoules each withabout 100 g or so. TMG and TEG are volatile liquids. The N-containinggas is usually ammonia (NH₃), and semiconductor quality NH₃ is availablein standard cylinders.

Alternately plasma-activated N₂, e.g., containing N ions or radicals,can be used as the N-containing gas. Molecular N₂ is substantiallyunreactive with GaCl₃ or GaCl even at high process temperatures.Nitrogen radicals can be prepared in a manner known in the art, ingeneral, by providing energy to split a nitrogen molecule, for example,by adding a RF source to a nitrogen line to generate anelectromagnetically induced plasma. When operating in this mode, thepressure in the reactor is usually reduced.

Of the known VPE processes, MOCVD and GaCl HVPE have been found to beless desirable for sustained, high Volume Manufacturing of Group IIInitride layers. First, MOCVD is less desirable for the growth of filmsgreater than 10 um because achievable deposition rates rate are lessthan 5% of the deposition rates achievable by HVPE processes. Forexample, HVPE deposition rate can be in the range of 100-1000 μ/hour ormore, while MOCVD rates are typically less than 10 μ/hour. Second, GaClHVPE is less desirable because this process requires that a supply ofliquid Ga be present in the reaction chamber in order to form GaCl byreaction with HCl. It has been found that maintaining such a supply ofliquid Ga in a form that remains reactive with HCl and that issufficient for high volume manufacturing is difficult.

Therefore, equipment of the invention is primarily directed to GaCl₃HVPE for high volume manufacturing. Optionally, it can also provide forMOCVD for, e.g., deposition of buffer layers and the like. However, useof GaCl₃ HVPE for high volume manufacturing requires a source of GaCl₃vapor that achieves a sufficient flow rate that can be maintainedwithout interruption (except for wafer loading/unloading in the reactionchamber) for a sufficient period. Preferably, an average sustaineddeposition rate is in the range of 100 to 1000 μm/hour of GaN per hourso that approximately one wafer (or one batch of multiple wafers)requires no more than one or two hours of deposition time for even thickGaN layers. Achieving such a preferred deposition rate requires that thesource provide a mass flow of GaCl₃ vapor at about approximately 250 or300 g/hour (a 200 mm circular 300 μm thick layer of GaN comprises aboutapproximately 56 g of Ga while GaCl₃ is about 40% Ga by weight).Further, such a flow rate can preferably be maintained for a sufficientduration so that production interruptions required to recharge/servicethe source are limited to at most one per week, or more preferably oneat least every two to four weeks. Accordingly, it is preferred that theflow rate can be maintained for at least 50 wafers (or batches ofmultiple wafers), and preferably for at least 100, or 150, or 200, or250 to 300 wafers or batches or more. Such a source is not known in theprior art.

The equipment of the invention provides a GaCl₃ source that overcomesproblems in order to achieve preferred flow rates and durations.Achieving preferred flow rates has been hindered in the past by certainphysical properties of GaCl₃. First, at ambient conditions, GaCl₃ is asolid, and vapor can be formed only by sublimation. However, it has beendetermined that GaCl₃ sublimation rates are inadequate for providingvapor at preferred mass flow rates. Second, GaCl₃ melts at about 78° C.,and vapor can then be formed by evaporation from the liquid surface.However, it has also been determined that evaporation rates areinadequate for providing preferred mass flow rates. Further, typicalphysical means for increasing rate of evaporation, e.g., agitation,bubbling, and the like, do not increase evaporation rate sufficientlybecause GaCl₃ liquid is known to be relatively viscous.

What is needed is a form of liquid GaCl₃ of sufficiently lowerviscosity, and it has been observed and discovered that beginning atabout approximately 120° C., and especially at about approximately 130°C. or above, GaCl₃ assumes such a lower viscosity state with a viscositysimilar to, e.g., that of water. And further, it has been observed anddiscovered that in this lower viscosity state, routine physical meansare capable of effectively raising the GaCl₃ evaporation ratesufficiently to provide the preferred mass flow rates.

Accordingly, the GaCl₃ source of this invention maintains a reservoir ofliquid GaCl₃ with temperature T1 controlled to about approximately 130°C. and provides physical means for enhancing the evaporation rate. Suchphysical means can include: agitate the liquid; spray the liquid; flowcarrier gas rapidly over the liquid; bubble carrier gas through theliquid; ultrasonically disperse the liquid; and the like. In particular,it has been discovered that bubbling an inert carrier gas, such as He,N₂ or H₂ or Ar, by arrangements known in the art through a lowerviscosity state of liquid GaCl₃, e.g., GaCl₃ at about 130° C., iscapable of providing the preferred mass flow rates of GaCl₃. Preferredconfigurations of the GaCl₃ source have increased total surface area inproportion to their volume in order to achieve better temperaturecontrol using heating elements outside of the reservoir. For example,the illustrated GaCl₃ source is cylindrical with a height that isconsiderably greater than the diameter. For GaCl₃, this would be around120 g per hour for a period of at least 48 hours, to 250 g per hour fora period of at least 100 hours, to 500 g per hour for a period of atleast one week, to as high as 750 to 1000 g per hour for a period of atleast a month.

Moreover, a GaCl₃ source capable of the preferred flow rate and durationcannot rely on GaCl₃ supplied in individual 100 g ampoules. Such anamount would be sufficient for only 15 to 45 minutes of uninterrupteddeposition. Therefore, a further aspect of the GaCl₃ source of thisinvention is large GaCl₃ capacity. To achieve the high-throughput goalsof this invention, the time spent recharging GaCl₃ source is preferablylimited. However, recharging is made more complicated by the tendency ofGaCl₃ to react readily with atmospheric moisture. The GaCl₃ charge, thesource, and the GaCl₃ supply lines must be free of moisture prior towafer production. Depending on the throughput goals of variousembodiments, the invention includes sources capable of holding at leastabout 25 kg of GaCl₃, or at least about 35 kg, or at least about 50 to70 kg (with an upper limit determined by requirements of size and weightin view of the advantages of positioning the source in close proximityto the reaction chamber). In a preferred embodiment, the GaCl₃ sourcecan hold between about 50 and 100 kg of GaCl₃, preferably between about60 and 70 kg. It will be realized that there is no real upper limit tothe capacity of the GaCl₃ source other than the logistics of itsconstruction and use. Furthermore, multiple sources of GaCl₃ could beset up through a manifold to permit switching from one source to anotherwith no reactor downtime. The empty source could then be removed whilethe reactor is operating and replaced with a new full source.

A further aspect of the GaCl₃ source of this invention is carefultemperature control of the supply lines between the source and thereaction chamber. The temperature of the GaCl₃ supply lines andassociated mass flow sensors, controllers, and the like preferablyincrease gradually from T2 at the exit from the source up to T3 atreaction chamber inlet 33 in order to prevent condensation of the GaCl₃vapor in the supply lines and the like. However, temperatures at thereaction chamber entry must not be so high that they might damagesealing materials (and other materials) used in the supply lines andchamber inlet, e.g., to seal to the quartz reaction chamber, forgaskets, o-rings, and the like. Currently, sealing materials resistantto Cl exposure and available for routine commercial use in thesemiconductor industry generally cannot withstand temperatures greaterthan about 160° C. Therefore, the invention includes sensing thetemperature of the GaCl₃ supply lines and then heating or cooling thelines as necessary (generally, “controlling” the supply linetemperatures) so that the supply line temperatures increase (or at leastdo not decrease) along the supply line from the source, which ispreferably at about approximately 130° C., up to a maximum at thereaction chamber inlet, which is preferably about approximately 145 to155° C. (or other temperature that is safely below the high temperaturetolerance of o-rings or other sealing materials). To better realize thenecessary temperature control, the length of the supply line between thesource apparatus and the reaction chamber inlet should be short,preferably less than about approximately 1 ft., or 2 ft. or 3 ft. Thepressure over the GaCl₃ source is controlled by a pressure controlsystem 17.

A further aspect of the GaCl3 source of this invention is precisecontrol of the GaCl3 flux into the chamber. In a bubbler embodiment, theGaCl3 flux from the source is dependent on the temperature of the GaCl3,the pressure over the GaCl3 and the flow of gas that is bubbled throughthe GaCl3. While the mass flux of GaCl3 can in principle be controlledby any of these parameters, a preferred embodiment is to control themass flux by varying the flow of a carrier gas by controller 21.Routinely-available gas composition sensors such as a Piezocor, and thelike 71 can be used to provide additional control of the actual GaCl3mass flux, e.g., in grams per second, into the reaction chamber. Inaddition, the pressure over the GaCl3 source can be controlled by apressure control system 17 placed on the outlet of the bubbler. Thepressure control system, e.g. a back pressure regulator, allows forcontrol of the over pressure in the source container. Control of thecontainer pressure in conjunction with the controlled temperature of thebubbler and the flow rate of the carrier gas facilitates an improveddetermination of precursor flow rate. Optionally, the container alsoincludes an insulating outer portion.

It is desirable that the materials used in the GaCl3 source, in theGaCl3 supply lines, and in the inlet manifold structures in contact withGaCl3 are chlorine resistant. For metal components, a nickel-based alloysuch as Hastelloy, or tantalum or a tantalum-based alloy is preferred.Further corrosion resistance for metal components can be providedthrough a protective corrosion resistant coating. Such coatings cancomprise silicon carbide, boron nitride, boron carbide, aluminum nitrideand in a preferred embodiment the metal components can be coated with afused silica layer or a bonded amorphous silicon layer, for exampleSILTEK® and SILCOSTEEL® (commercially available from Restek Corporation)has been demonstrated to provide increased corrosion resistance againstoxidizing environments. For non-metal components, chlorine resistantpolymeric materials (either carbon or silicone polymers) are preferred.

In view of the above, a preferred GaCl3 source capable of holdingpreferred amounts of GaCl3 is referred to herein as acting“continuously” in that, in an appropriate embodiment, the source candeliver its contained GaCl3 without interruption to deliver the desiredamounts for the recited time durations. It should be understood,however, that, in a particular embodiment, the reaction chamber (orother component of the present system) is or can be so constructed orcertain process details are performed, so that intermittent chambermaintenance, e.g., cleaning and so forth, is required. In contrast, theGaCl3 source is configured and dimensioned to provide the desiredamounts of the precursor in an uninterrupted manner to facilitate highvolume manufacture of the Group III-V product. Thus, the source iscapable of providing these amounts without having to be shut down orotherwise discontinued for replenishment of the solid precursor.

This can be achieved either by providing sufficiently large quantitiesof the solid precursor in a single reservoir, or by providing multiplereservoirs that are manifolded together. Of course, a skilled artisanwould understand that in a manifolded system, one reservoir can beoperated to provide the gaseous precursor while one or more otherreservoirs are being replenished with solid precursor material, and thatthis remains an uninterrupted system since it has no affect on theoperation of the reactor. In such embodiments, the GaCl3 source is alsoreferred to herein as acting continuously in that the source can deliverits contained GaCl3 without refilling, opening, cleaning, replenishingor other procedure during which the source is not fully functional. Inother words, the source does not by itself necessitate interruption ofGaN deposition.

Also, as described, a preferred GaCl3 source can contain GaCl3 in asingle reservoir. Also, a preferred source can include multiplereservoirs (i.e., 2, 5, 10 etc.) having outlets which are manifolded sothat GaCl3 vapor can be delivered from the multiple reservoirs insequence or in parallel. In the following, both embodiments are oftenreferred to as a single source. In preferred embodiments, the equipmentof this invention can also provide for sources for Group III metalorganic compounds so that MOCVD processes can be performed. For example,MOCVD can be used to, e.g., deposit thin GaN or AlN buffer layers, thinintermediate layers, layers of mixed metal nitrides, and so forth.Additional process gases can be routinely supplied as known in the art.

The group V precursor is a gas containing one or more Group V atoms.Examples of such gases include NH₃, AsH₃ and PH₃. For the growth of GaN,NH₃ is typically used because it can provide sufficient incorporation ofN at typical growth temperatures. Ammonia and other N precursors areexternal sources. For example, semiconductor grade NH₃ is readilyavailable in cylinders 19 of various sizes, and carrier gases 72 areavailable as cryogenic liquids or as gases, also in containers ofvarious sizes. Fluxes of these gases can be routinely controlled by massflow controllers 21 and the like. In alternative embodiments, theequipment of this invention can also provide for sources of other GroupIII chlorides.

2. Reactor Geometry

Next, to achieve increased economy, the reactor subsystems arepreferably adaptations of commercially available reactor systems.Available reactors preferred for adaptation and use in this inventioninclude as-is most or all of the features to be next described. Thesefeatures have been determined to be useful for HVM of GaN layers withthe modifications and enhancements disclosed herein. Although thefollowing description is directed mainly to embodiments that adaptexisting equipment, reactors and reactor systems can be purpose built toinclude the to-be-described features. The invention includes bothredesigning and modifying existing equipment and designing andfabricating new equipment. The invention also includes the resultingequipment.

Generally, preferred reaction chambers have horizontal process-gas flowand are shaped in an approximately box-like or hemi-sphere likeconfiguration with lesser vertical dimensions and greater horizontaldimensions. Certain features of horizontal reaction chambers areimportant in limiting unproductive reactor time and achieving HVM ofquality GaN wafers.

3. Low Thermal Mass Susceptor and Lamp Heating

First, time spent ramping-up temperature after introducing new wafersand time spent ramping-down temperature after a deposition run is notproductive and should be limited or minimized. Therefore, preferredreactors and heating equipment also have lower thermal masses (i.e.,ability to absorb heat quickly), and the lower the thermal masses themore preferred. A preferred such reactor is heated with infrared (IR)heating lamps and has IR transparent walls FIG. 1 illustrates reactor 25made of quartz and heated by lower longitudinal IR lamps 27 and uppertransverse IR lamps 29. Quartz is a preferred chamber wall material,since it is sufficiently IR transparent, sufficiently Cl resistant, andsufficiently refractory.

4. Closed Loop Temperature Control on Chamber Walls and Flanges

Time spent cleaning reaction chamber interiors is also not productiveand also should be limited or minimized. During GaN depositionprocesses, precursors, products, or byproducts can deposit or condenseon interior walls. Such deposition or condensation can be significantlylimited or abated by controlling the temperature of the chamber wallsgenerally by cooling them to an intermediate temperature that issufficiently high to prevent condensation of precursors and byproducts,but that is sufficiently low to prevent GaN formation and deposition onthe walls. Precursors used in GaCl₃ HVPE processes condense at belowabout 70 to 80° C.; the principal byproduct, NH₄Cl, condenses only belowabout 140° C.; and GaN begins to form and deposit at temperaturesexceeding about 500° C. Chamber walls are controlled to temperature T5that is preferably between 200° C., which has been found to besufficiently high to significantly limit precursor and byproductcondensation, and 500° C., which has been found to be sufficiently lowto significantly limit GaN deposition on chamber walls. A preferredtemperature range for the chamber walls is 250 to 350° C.

Temperature control to preferred ranges generally requires coolingchamber walls. Although IR transparent, chamber walls are neverthelessheated to some degree by heat transferred from the high temperaturesusceptor. FIG. 1 illustrates a preferred cooling arrangement in whichreaction chamber 25 is housed in a full or partial shroud 37 and coolingair is directed through the shroud and over and around the exterior ofthe reaction chamber. Wall temperatures can be measured by infraredpyrometry and cooling air flow can be adjusted accordingly. For example,a multi-speed or a variable speed fan (or fans) can be provided andcontrolled by sensors sensitive to chamber wall temperatures.

5. Load Lock, Cassette to Cassette

Wafer loading and unloading time is also not productive. This time canbe routinely limited by automatic equipment schematically illustrated at39. As it known in the art, this equipment can store wafers, load wafersinto, and unload wafers from the reaction chamber, and generallycomprises, e.g., robotic arms and the like that move wafers, e.g., usingtransfer wands, between external holders and the susceptor in thereaction chamber. During wafer transfer, the reaction chamber can beisolated from ambient exposure by intermediate wafer transfer chambers.For example, controllable doors between the transfer chamber and theexterior can permit loading and unloading and can then seal the transferchamber for ambient exposure. After flushing and preparation, furthercontrollable doors between the transfer chamber and the reactor can opento permit placement and removal of wafers on the susceptor. Such asystem also prevents exposure of the reactor interior to oxygen,moisture or other atmospheric contaminants and reduces purging timesprior to load and unload of wafers. It is preferred to use a quartzBernoulli transfer wand because it reduces unproductive time by allowinghandling of hot wafers without causing contamination.

6. Separate Injection

Process gas flow control, from inlet manifold 33 in the direction ofarrow 31 to outlet manifold 35, is important for depositing high qualityGaN layers. This flow includes the following preferred characteristicsfor the process gases. First, the gallium containing gas, e.g., GaCl₃,and the nitrogen containing gas, e.g., NH₃, preferably enter thereaction chamber through separate inlets. They should not be mixedoutside the reaction chamber because such mixing can lead to undesirablereactions, e.g., forming complexes of GaCl₃ and NH₃ molecules, thatinterfere with subsequent GaN deposition.

Then, after separate entry, the GaCl₃ and NH₃ flows are preferablyarranged so that the gas has a uniform composition in space and timeover the susceptor. It has been found that the III/V ratio should varyover the face of the susceptor (and supported wafer or wafers) at anyparticular time preferably by less than approximately 5%, or morepreferably by less than approximately 3% or 2% or 1%. Also, the III/Vratio should be similarly substantially uniform in time over allportions of the face of the susceptor. Accordingly, the GaCl₃ and NH₃velocity profiles should provide that both gases both spread laterallyacross the width of the reaction chamber so that upon arriving at thesusceptor both gases have a non-turbulent flow that is uniform acrossthe width of the reaction chamber and preferably at least across thediameter of the susceptor.

Finally, the flow should not have recirculation zones or regions ofanomalously low flow rates, where one or more of the process gases canaccumulate with an anomalously high concentration. Localized regions oflow gas flow, or even of gas stagnation, are best avoided.

Preferred process gas flow is achieved by careful design or redesign ofthe inlet manifold of a new or existing reaction chamber. As used herethe term “inlet manifold” refers to the structures that admit processand carrier gases into a reaction chamber whether these structures areunitary or whether they comprise two or more physically separate units.

Inlet manifold designed and fabricated to have the following generalfeatures have been found to achieve preferred process gas flows.However, for most embodiments, it is advantageous for the gas flow intoa selected reaction chamber produced by a proposed inlet manifold designto be modeled using fluid dynamic modeling software packages known inthe art. The proposed design can thereby be iteratively improved toachieve increased uniformity prior to actual fabrication.

First, it has been found advantageous that process gas entry into thereaction chamber be distributed across some, most or all of the width ofthe chamber. For example, multiple gas inlet ports or one or more slotsthrough which gas can enter can be distributed laterally across thewidth of the chamber. A carrier gas such as nitrogen or hydrogen can beintroduced to assist in directing the GaCl₃ and the NH₃ gases throughthe reactor to the desired reaction location above the susceptor.Further, to prevent spurious deposition in the vicinity of the inletports, it is advantageous for the actual inlet ports to be spaced withrespect to the heated susceptor so that they are not heated aboveapproximately 400-500° C. Alternately, the inlet ports can be cooled orcan be spaced apart so the process gases do not mix in their vicinity.

Next it has been found that gas flow properties produced by a particularconfiguration of the GaCl₃ and NH₃ inlets can be improved, or “tuned”dynamically. Secondary purge gas flows impinging on or originating forexample from under the susceptor and mixing with the primary GaCl₃, andNH₃ flows can be used to alter these flows to increase uniformity ofcomposition and velocity or prevent deposition on reactor components.For example, in embodiments where the GaCl₃ and NH₃ flows enter thereaction chamber from different inlets, it has been found advantageousto provide a purge gas flow entering into the reaction chamber somewhatupstream of GaCl₃, and NH₃ flows to confine the process gases above theintended deposition zone and to shield the side walls of the reactorfrom unintended deposition. For these purposes, it is advantageous tointroduce a greater amount of carrier gas laterally near the chamberwalls and a lesser amount centrally about the middle of the chamber.

Also, preferred inlet manifolds provide for dynamic adjustment of, atleast, one of the process gas flows so that non-uniformities observedduring operation can be ameliorated. For example, inlets for a processgas can be divided into two or more streams and individual flow controlvalves can be provided to independently adjust the flow of each stream.In a preferred embodiment, GaCl₃ inlets are arranged into five streamswith independently controllable relative flow.

Further aspects of a preferred inlet manifold include temperaturecontrol. Thereby, inlet manifold temperatures T3 can be controlled bothto prevent the condensation of precursors, e.g., GaCl₃, and to preventdamage to temperature-sensitive materials, e.g., gasket or O-ringmaterials. As discussed, the GaCl₃ inlet ports should be at atemperature no less than the highest temperatures reached in the GaCl₃supply line, which is preferably increased from about approximately 110°C. to about approximately 150° C. Commercially availablechlorine-resistant, sealing materials, such as gasket materials andO-ring materials, available for use in the inlet manifold, in particularfor sealing the manifold to the quartz reaction chamber, begin todeteriorate at temperatures in excess of about approximately 160° C.Chlorine-resistant sealing materials such silicone o-rings usable tohigher temperatures, if available, can also be used, in which case theinlet manifold upper temperature limit can be raised.

Accordingly, inlet manifold temperature T3 should be controlled toremain in the range of about approximately 155 to 170° C. by eithersupplying heat to raise the temperature from ambient or removingtransferred heat from the hot reaction chamber and very hot susceptor.In preferred embodiments, an inlet manifold includes temperature sensorsand channels for temperature control fluids. For example, temperaturesof 155 to 170° C. can be achieved by circulating atemperature-controlled GALDEN™ fluid. Other known fluids can be used forother temperature ranges. The fluid channels preferably run in proximityto the temperature sensitive portions of the inlet manifold, e.g., theGaCl₃ inlet ports and sealing o-rings. Channel arrangement can be chosenmore precisely in view of thermal modeling using software packages knownin the art.

GaCl₃ molecules whether in the solid or liquid or vapor phase are knownto exist mainly in the Ga₂Cl₆ dimer form. That form is actually verystable up to 800° C., Thermodynamic calculations corroborated by gasphase Raman spectroscopy have confirmed that at 300° C. more than 90% ofthe gas phase is composed of the dimer molecule and at 700° C. more than99% of the dimer has decomposed into the GaCl₃ monomer.

As the dimer molecule is injected through a metallic injection port keptat temperatures at or below 150° C., the decomposition of the dimer willoccur only in contact with the hot susceptor which is at temperatureabove 1000° C. Depending on the velocity of the gas above the susceptoror its residence time the portion of the dimer that will be decomposedmight be too small to sustain a high growth rate on the wafer. The GaNdeposition process proceeds through the adsorption of GaCl₃ and itsfurther decomposition to GaCl_(x) with x<3 until all chlorine has beenremoved to obtain an adsorbed atom of Ga. It is therefore desired tooperate from the monomer form of GaCl₃. A preferred embodiment of theinvention introduces the dimer through a quartz tube under the reactorchamber situated upstream of the susceptor region. This quartz tubeconnects to the reactor chamber through a funnel with an ovalcross-section. Energy is provided to the dimer while in the funnel todecompose the dimer to the monomer. A preferred embodiment uses IRradiation from IR lamps located and shaped in such a way that the quartztube and funnel receive a high flux of IR radiation. In this embodiment,the funnel region is filled with IR absorbent materials and theradiation power adjusted to bring the IR absorbent material to atemperature of 600° C. or more preferably 700° C. or higher. As thedimer form of GaCl₃ is injected in the quartz injector and passesthrough the hot funnel zone, the dimer will be decomposed to the monomerand be injected in the reaction chamber just upstream of the susceptor.Preferably the region between the injection point of the GaCl₃ into thereactor and the susceptor is maintained at a temperature above 800° C.to prevent the re-formation of the dimer. A preferred embodiment is touse a SiC plate between the funnel and the susceptor which is heated bythe IR heating lamps to maintain a temperature above 700° C. andpreferably above 800° C.

7. Susceptor and Multi-Wafer Susceptor

The susceptor and its mounting can be of standard construction asgenerally known in the art. For example, it can comprise graphite coatedwith silicon carbide or silicon nitride, or alternatively, a refractorymetal or alloy. The susceptor is preferably mounted for rotation on ashaft. During GaN deposition, susceptor temperatures T4 can beapproximately 1000 to 1100° C. (or higher) and are maintained by thequartz IR lamps controlled by known temperature control circuitry. Toavoid forming a dead zone beneath the susceptor, the susceptor mountingpreferably provides for injection of purge gas. This injection is alsoadvantageous because it can limit or minimize unwanted deposition on theunderside of the heated susceptor and of adjacent components that mayalso be heated (directly or indirectly). The susceptor can be configuredto hold one or more substrates.

8. Heated Exhaust

Reaction chamber outlet manifold 35 provides for the free andunobstructed flow of exhaust gases from the reaction chamber through theexhaust lines 41 and to waste abatement system 5. The exhaust system canalso include a pump (42) and associated pressure control system(pressure control valve (44), pressure gauge (46) and associated controlequipment to permit operation at reduced pressure). The outlet manifoldexhaust lines and pressure control equipment (if used) areadvantageously also temperature controlled to limit condensation ofreaction products. Exhaust gases and reaction products typicallycomprise the carrier gases; un-reacted process gases, GaCl₃ and NH₃;reaction byproducts which are primarily NH₄Cl, NH₄GaCl₄, HCl, and H₂. Asdescribed above, temperatures above about approximately 130° C. arerequired to prevent condensation of GaCl₃. NH₄Cl condenses into apowdery material below about approximately 140° C., and the outletmanifold and exhaust system should be kept above this temperature. Onthe other hand, to prevent deterioration of sealing materials, theoutlet manifold temperature should not exceed about approximately 170°C.

Accordingly, outlet manifold temperature T6 is preferably maintained inthe range of about approximately 155 to 170° C. by temperature controlmeans similar to those used for inlet manifold temperature control(including optional thermal modeling). Maximum exhaust line temperatureT7 is limited by the maximum allowable temperature for the seals,preferably in the range of about 155 to 170° C.

9. Waste Management

Considering next waste abatement subsystems 5, a preferred abatementsystem can assist in economical operation of the invention by recoveryof waste gallium compounds exhausted from the reaction chamber. A singleembodiment of the invention can exhaust 30 kg, or 60 kg, or more during(assuming approximately 50% waste) during a month of sustained, highvolume manufacturing. At current Ga prices, it is economical to recoverthis waste Ga and recycle it into GaCl₃ precursor, thereby achievingeffectively approximately 90 to 100% Ga efficiency.

FIG. 1 also schematically illustrates a preferred embodiment of wasteabatement subsystem 5 that provides for gallium recovery and that can bereadily adapted from commercially available products. The streamexhausted from reaction chamber 25 passes through exhaust lines 41temperature controlled at T7 to limit condensation of exhaust products,e.g., in the range of about 155 to 170° C. or greater as convenient, andthen into burner unit 43. The burner unit oxidizes the exhaust gases bypassing it through high temperature combustion zone 45 comprising, e.g.,H₂/O₂ combustion. The oxidized exhaust stream then passes through tube47 into countercurrent water scrubber unit 49 where it moves in acountercurrent fashion with respect to water stream 51. The water streamremoves substantially all water soluble and particulate components fromthe oxidized exhaust stream. The scrubbed exhaust gas is then releasedfrom the system 57.

The water stream with the soluble and particulate materials passes toseparator 59 where particulate components, primarily particulate galliumoxides (e.g., Ga₂O₃), are separated 61 from the water solublecomponents, primarily dissolved NH₄Cl and HCl. Separation can beobtained by known techniques, such as screening, filtering,centrifugation, flocculation, and so forth. A single embodiment of theinvention can produce 60 kg, or up to 120 kg, or more, of particulateGa₂O₃ during each month of operation. The particulate gallium oxidesgallates are collected and the Ga is advantageously recovered andrecycled into, e.g., GaCl₃ by known chemical techniques: see, e.g.,Barman, 2003, Gallium Trichloride, SYNLETT 2003, no. 15, p. 2440-2441.The water-soluble components are passed from the system.

10. Gate Valve

A gate valve seals the reactor chamber interior from the exterior, whichis often the interior of a transfer chamber. The gate valve and reactorchamber loading port, are preferably sized and configured so that whenthe gate vale is open, an automated wafer-transfer device can freelytransfer wafers between the reactor chamber and the transfer chamber.When closed, the gate valve in cooperation with an opposed face of thereactor chamber seal the interior of the reactor chamber. In thefollowing, gate valves of this invention are generally describedfollowed by more detailed description in view of FIGS. 7A-B and 8A-C.Arrangement of a gate valve of this invention in a reactor system ofthis invention is in a subsequent section in view of FIGS. 4 and 6.

Gate valves of this invention preferably include one or more gas portsand one or more temperature control mechanisms. Also, gate valves, orthe opposed face of a reactor assembly, or both, include sealingmaterials arranged to actually accomplish and complete a tight sealbetween the reactor chamber interior and exterior.

Concerning gas ports, one or more gas ports are preferably provided andarranged to admit one or more species of selected gases (usually, onespecies) into a sealed reactor chamber, that is the gas ports arearranged across the face of the gate valve exposed to the reactorinterior (equivalently, the exposed face). The arrangement can comprisepatterns that place gas ports uniformly or non-uniformly across theexposed face. For example, in a non-uniform arrangement, the ports canbe concentration towards the center of the exposed face, or concentratedtowards one or both lateral sides of the exposed face, or in othernon-uniform arrangements. Patterns of ports can comprise squarelattices, rectangular lattices, hexagonal lattices, single rows,multiple rows, and the like.

In preferred embodiments, the ports are arranged in one or more parallelrows (equivalently, in a square or rectangular pattern) extending acrossthe exposed face of the gate valve. They can be uniformly distributedacross the exposed face or concentrated at the lateral sides of theexposed face. A gas (preferably one or more relatively inert gases) canbe admitted through the ports in order to reduce unwanted deposits onthe side walls of the reactor chamber, to reduce gas recirculationwithin the reactor chamber, and to reduce residence times of precursorand product gases in the reactor chamber. In addition, gas admittedthrough the ports can act to limit contact (and protect) between theexposed face of the gate valve and the process gases within the reactorchamber (i.e., the gas acts as a shield of the exposed face).

Concerning temperature control mechanisms, temperature control of thegate valve is an advantage of the present invention for the followingreasons. First, the portion of the gate valve exposed to the reactorchamber (equivalently, exposed face) is preferably maintained at a highenough temperature so that gases in the reactor do not condense on theexposed face and so that unwanted reactions or complex formation are notinduced in the gases in the reactor by contact with the exposed face.Second, the portions of the gate valve that physically oppose and form aseal with corresponding portions of the entrance assembly of the reactor(equivalently, the sealing portion of the gate valve and the sealingportions of the reactor assembly) are preferably maintained at a lowenough temperature so that thermal damage to auxiliary components of theunit, e.g., o-rings, seals, gaskets, etc, is limited or prevented. Also,the temperature of the exposed face should remain below thedeposition/reaction temperatures, but this is virtually always the case.

High and low temperature thresholds depend on the particular processbeing conducted in a reactor chamber. In the case of HVPE growth of GaN,significant temperature thresholds include: the condensation temperatureof reaction precursor GaCl₃ at or below ≈80° C. into a liquid form; thecondensation temperature of reaction product NH₄Cl at or below ≈140-150°C. into a solid form (i.e., the reverse of sublimation); and the safeoperating temperatures of currently-available, chlorine-resistantsealing materials at or below ≈150-160° C. (here, “≈” is a commonmathematical symbol used herein with its common meaning of about orapproximately).

Preferred gate valve assemblies (e.g., a combination of a gate valve andtemperature control mechanisms) comprise both mechanisms capable ofraising the temperature of an exposed face of the gate valve andlowering the temperature of a sealing portion. Further embodiments,however, can comprise only a temperature raising mechanism, or atemperature lowering mechanism, or neither. Further embodiments cancomprise multiple mechanisms of either type. Also, temperature controlmechanisms can be integral to the gate valve, or integral (or closelyadjacent) to the sealing portion of the reactor, or external to butassociated with the gate valve or the reactor, or a combination of sucharrangements. In the following, preferred, but non-limiting, temperaturecontrol mechanisms are described. However, the invention can includetemperature mechanism other than those described.

The exposed face of a gate valve can be heated by conduction from thebody of the gate valve, which in turn can be heated by a numbertemperature control devices known to those with ordinary skill in theart, including but not limited to, resistance heating, inductionheating, radiant heating, high temperature gas/liquid heating etc. Inone preferred embodiment, the body (and thereby also the exposed face)of the gate valve can be heated and controlled by radiant heatingelements (e.g., infrared elements) comprising either filament lamps orsolid state devices or a combination thereof. The radiant heatingelements are preferably placed external to the reactor chamber (e.g., inthe transfer chamber), because of the high temperatures and corrosiveenvironment within the reactor chamber. The radiant IR heating elementscan be arranged in the transfer chamber to be in close proximity to thegate valve for providing heating specifically directed to the unit sothat the exposed face is at a high enough temperature to preventcondensation.

In an alternative preferred embodiment, the temperature of the exposedface of the gate valve assembly can be raised and controlled by thecirculation of a heated fluid, e.g., a high temperature gas, through thebody of the gate valve. The heated gas can be arranged to flow intopassageways in the body of the gate valve, through the passageways, andthen out for reuse or disposal. Further, heated gas in the passagewayscan be directed through some or all of the plurality of ports in theexposed face of the gate valve. Preferably, internal gas passageways arearranged to be near the exposed face so that the heated gas circulatingthrough the body of the fixture imparts heating to the unit raising thetemperature of the exposed face to a desired level to combat the buildup of unwanted reactor deposits.

The sealing portion of the gate valve can be cooled directly orindirectly by, e.g., circulating cool fluids, including cool gases orcool liquids. In one preferred embodiment, cool fluids can be circulatedin passageways within the sealing portion of the reactor and adjacent tothe sealing materials or to the sealing portion of the gate valve.Alternatively, cool fluids can be circulated within the body of the gatevalve in passageways in proximity to the sealing portion of the gatevalve. In another preferred embodiment, cool gas can be circulated inpassageways within the gate valve. Alternatively, cool gas flows can bedirected towards the body of the gate valve from ports in the transferchamber. The sealing portion of the gate valve is then cooled byconduction from the body exposed in the transfer chamber. For example,ambient gas can be removed from the transfer chamber, cooled, and thenreintroduced into the transfer chamber and directed towards the gatevalve.

In various embodiments, a gate valve assembly can include only one ormore temperature control devices for raising the temperature of theexposed face, or only one or more temperature control devices forlowering the temperature of the sealing face, or one or more of bothtypes of temperature control devices. An advantageous combinationincludes a temperature control device for raising the temperature of theexposed face together with a temperature control device for lowering thetemperature of the sealing face. For example, the temperature of theexposed face can be raised by circulating high temperature gas throughpassageways in the gate valve body (and out of the gate valve ports intothe reactor), and the temperature of the sealing face can be lowered bycirculating low temperature fluid (e.g., in the sealing portion of thereactor or gate valve). Another exemplary combination includescirculating a heated gas through passageways in the gate valve body butcontrolling the temperature of the heated gas so that the temperature ofthe exposed face is sufficiently high but the temperature of the sealingportion is not raised above its thermal damage threshold.

A gate valve assembly preferably includes one or more thermocouples toprovide feedback by which the heating and/or cooling mechanisms can beadjusted to maintain the temperature of the exposed face of the gatevalve sufficiently high and to maintain the temperature of the sealingportion sufficiently low. Thermocouples can be situated in and aroundthe gate valve assembly in the transfer chamber and also in the reactorchamber.

FIG. 7A schematically illustrates an exemplary arrangement of a gatevalve of this invention within a typical CVD system. This figureillustrates transfer chamber 703 adjacent to reactor chamber 713; rearfaceplate assembly 725 of the reactor chamber bounding both the transferchamber and the reactor chamber; and a loading port between the twochambers sized to permit material transfers. A gas, often a precursorgas, can be introduced into the reactor though port 715 which isillustrated as opening into the loading port between the chambers. As inthe applications to be discussed with reference to FIGS. 5 and 6, thereactor chamber often comprises quartz walls and is operated in acold-wall manner.

The loading port between the chambers is sealed by gate valve 702. Thegate valve is here illustrated in a closed position; its open positionis indicated by dotted outline 705. Passage 719, a transfer opening,assumes position 719′ when the gate valve is open, and in this positionis aligned with the reactor loading port so that material can betransferred through this transfer opening and then through the loadingport without hindrance. Thereby, the gate valve will not interfere withmaterial transfer between the chambers. Many mechanisms can be employedto open and close the gate valve; illustrated here is a genericmechanism 704 which rotates the gate valve about pivot 711.

Preferably, as illustrated, the gate valve is also provided withinternal passageways and a plurality of ports 707 through which gas canenter the reactor chamber.

Preferably, the seal formed by contact of the sealing portion of thegate valve with the sealing portion of the reactor chamber is completedand augmented by sealing materials formed as gaskets, O-rings, and thelike, and arranged between the opposing sealing portions. Such sealingmaterials are generically illustrated as seals 717-1 and 717-2. In thecase of HVPE manufacture of GaN, the sealing materials are preferablyresistant both to chlorine compounds and to temperatures up to athreshold ≈150-170° C. (or higher if such sealing materials becomeavailable).

FIG. 7B illustrates in cross-section gate valve 702. A gate valve pivotshaft can extend through opening 711. Transfer opening 709 provides formaterial transfer as described. The gate valve include internalplenum-like gas passageway 707 leading to a plurality of ports 707 inthe face of the valve. Recesses 717-1 and 717-2 are for retaining anO-ring encircling the exposed face of the gate valve. An O-ring can alsobe held by faceplate assembly 725.

FIG. 7A also illustrates several gate-valve temperature controlmechanisms. The gate valve, and thereby the exposed face of the gatevalve, can be heated by exemplary heating lamp 701, e.g., an IR heatinglamp. An absorptive coating can be placed on the rear portion of thegate valve. Alternatively, two of more heating lamps can be used whichcan be placed in different locations, or in multiple locations, aroundthe gate valve. The exposed face of the gate valve can also be heatedpassing hot gas through gas passageways 707 interior to the valve body.Preferably some or all of the heated gas passes into the reactor chamberthrough ports 707 in the exposed face.

Sealing materials 717-1 and 717-2 are arranged between the sealingportions of gate valve 702 and the sealing portions of reactor faceplateassembly 725. These materials can be cooled by circulating coolingfluids either within the gate valve or within the faceplate assembly (orwithin both). Here, cooling fluid passageways 721-1 and 721-2 areillustrated in the faceplate assembly adjacent to sealing materials717-1 and 717-2. These cooling mechanisms preferably cool primarilyregions of the gate valve and faceplate in the vicinity of the sealingmaterials. Cooling mechanisms are preferably omitted if sealingmaterials can resist expected temperatures, or are not needed at all.

For completeness, also illustrated are seals between reactor chamber 713and faceplate assembly 725 which are also completed and augmented bysealing materials 719-1 and 719-2. These latter sealing materials can beprotected, if necessary, from high reactor temperatures by circulatingcooling fluid in passageways 723-1 and 723-2.

Thermocouples (not illustrated) can be arranged in and around the gatevalve and adjacent portions of the reactor assembly to provide feedbackby which the heating and/or cooling devices can be adjusted. Preferably,such temperature feedback reflects the temperature of the exposed faceso that this temperature can be maintained sufficiently high, and alsoreflects the temperature of the sealing materials so that thistemperature can be maintained sufficiently low.

This invention includes embodiments of gate valves having a plurality ofdischarge ports in the exposed face for discharging gas, one or moreinlet ports for receiving gas, especially heated gas, and internalpassageways connecting inlet and discharge ports. FIGS. 8A-C illustratethree gate valve embodiment, each having different number andarrangement of these ports. The three illustrated embodiments are notlimiting; the invention includes other numbers and arrangements. Commonelements of all three illustrated gate valves include: pivot openingsand shafts 828, transfer openings 821-1, 825-2, and 825-3, and O-ringseals 829-1, 829-2, and 829-3.

First concerning discharge ports, FIG. 8A illustrates a gate valve witha single row of discharge ports 821-1 arranged with greater numberstowards both lateral peripheries of exposed face gate valve and withlesser numbers in the vicinity of the center of the exposed face. FIG.8B illustrates a gate valve with a regular, rectangular arrangement ofdischarge ports aligned in three, parallel row and occurring in constantnumbers across the entire exposed face. FIG. 8C illustrates a variationof the arrangement of FIG. 8B in which extra discharge ports arearranged in the regions at the lateral edge of the exposed face thatwere occurring by inlet ports in FIG. 8B.

Concerning inlet ports, gate valve construction is simplified if gas canbe circulated into passageways within the gate valve from passageways inthe faceplate assembly of the reactor chamber. When the gate valve isclosed, the openings of one or more passageways in the faceplateassembly can become aligned with the openings of one or morecorresponding passageways in the gate valve. The junction between thesepassageways can be sealed by O-rings and the like. FIGS. 8A and 8Cillustrate gate valves each with two such ports, 827-1 and 827-3,arranged at both lateral edges of the sealing portion of the gate valveand outside of O-rings 821-1 and 821-3. Being outside of these O-rings,any gas that escapes from between these passageway seals escapes intothe transfer chamber. FIG. 8B illustrates a gate valve with two suchports, 827-2, arranged at both lateral edges of the sealing portion ofthe gate valve but inside of O-ring 821-2. Being inside of this O-ring,any gas that escapes from between the inlet passageway seals escapesinto the reactor chamber.

A Preferred Particular Embodiment of the Invention

Next described is a particular preferred embodiment of the inventionthat has been generally described above. This embodiment is based on themodification and adaptation of an EPSILON® series, single-waferepitaxial reactor from ASM America, Inc. Accordingly many of thefollowing features are specific to this preferred particular embodiment.However, these features are not limiting. Other particular embodimentscan be based on modification and adaptation of other available epitaxialreactors and are within the scope of the invention.

FIGS. 2A-C illustrate aspects of GaCl₃ delivery system 101 includingreservoir 103, which can hold 50 to 75 kg of GaCl₃ and can maintain itat as a liquid at a controlled temperature of up to about approximately130 to 150° C., and supply assembly with supply lines, valves andcontrols 105, which provide a controlled mass flow of GaCl₃ to thereactor chamber while limiting or preventing GaCl₃ condensation withinthe lines. The reservoir includes internal means for enhancingevaporation of the liquid GaCl₃. In a preferred embodiment, theseinclude a bubbler apparatus as known in the art; in alternativeembodiments, these can include means for physical agitation of the GaCl₃liquid, for spraying the liquid, for ultrasonic dispersal of the liquid,and so forth. Optionally, the supply line (or delivery line) includes acoaxial portion having an inner line conveying the carrier gas and theGroup III precursor and an enclosing coaxial line providing an annularspace inside the enclosing line but outside the inner line. The annularspace can contain a heating medium.

FIG. 2C illustrates an exemplary arrangement of delivery system 101 incabinet 135 which is positioned adjacent to conventional process gascontrol cabinet 137. To limit the length of the GaCl₃ supply line,cabinet 135 is also positioned adjacent to the reaction chamber, whichhere is hidden by cabinet 137. Process gas control cabinet 137 includes,for example, gas control panel 139 and separate portions 141-147 foradditional process gases or liquids, such as a Group III metal organiccompounds.

FIG. 2B illustrates preferred supply assembly 105 in more detail. Valves107 and 109 control lines that conduct carrier gas into reservoir 103,then through the internal bubbler in the reservoir, and then out fromthe reservoir along with evaporated GaCl₃ vapor. They can isolate thereservoir for maintenance and so forth. Valve 110 facilitates thepurging of the system above the outlet and inlet values of the containersystem. In particular, since condensation can possibly occur in thepig-tail elements 111, 112, valve 110 is useful in order to purge theseareas. Control of the container pressure in conjunction with thecontrolled temperature of the bubbler and the flow rate of the carriergas facilitates improved determination of precursor flow rate. Theaddition of valve 110 allows the complete delivery system to be purgedwith non-corrosive carrier gas when not in growth mode, thereby reducingexposure of the system to a corrosive environment and consequentlyimproving equipment lifetime. The assembly also includes valves 111-121for controlling various aspects of flow through the supply lines. Italso includes pressure controller and transducer 129 to maintain aconstant pressure over the GaCl3 container. Also provided is a mass flowcontroller 131 to provide a precise flow of carrier gas to the GaCl3container. These act to provide a controlled and calibrated mass flow ofGaCl3 into the reaction chamber. It also includes pressure regulators125 and 127. The supply line assembly, including the supply lines,valves, and controllers, is enclosed in multiple aluminum heating blocksin clamshell form to enclose each component. The aluminum blocks alsocontain temperature sensors that control supply line componenttemperatures so that the temperature increases (or at least does notdecrease) from the output of the reservoir up to the inlet of thereaction chamber. A gas heater is provided to heat the inlet gas to theGaCl3 source, preferably to a temperature of at least 110° C.

Optionally, a purifier capable of removing moisture from the carrier gasdown to no more than 5 parts per billion is placed in a carrier gasinlet line, and further a carrier gas filter is downstream of thecarrier gas purifier. The carrier gas can be optionally configured withsinusoidal bends, e.g., pigtail 112, for providing increased heatexchange surface proximate to the carrier gas heater.

FIGS. 3A and 3B illustrate top views of a preferred embodiment of thereaction chamber 201. This reaction chamber has quartz walls and isgenerally shaped as an elongated rectangular box structure with agreater width and lesser height. A number of quartz ridges 203 spantransversely across the chamber walls and support the walls especiallywhen the chamber is operated under vacuum. The reaction chamber isenclosed in a shroud that directs cooling air in order that the chamberwalls can be controlled to a temperature substantially lower than thatof the susceptor. This shroud generally has a suitcase-like arrangementthat can be opened, as it is in these figures, to expose the reactionchamber. Visible here are the longer sides 205 and the top 207 of theshroud. Susceptor 215 (not visible in this drawing) is positioned withinthe reactor. The susceptor is heated by quartz lamps which are arrangedinto two arrays of parallel lamps. Upper lamp array 209 is visible inthe top of the shroud; a lower array is hidden below the reactionchamber. Portions of the inlet manifold are visible.

FIG. 3C illustrates a longitudinal cross-section through particularpreferred reaction chamber 301 but omitting for strengthening ribs 203.Illustrated here are top quartz wall 303, bottom quartz wall 305 and onequartz side wall 307. Quartz flange 313 seals the inlet end of thereaction chamber to the inlet manifold structures, and quartz flange 309seals the outlet end of the reaction chamber to the outlet manifoldstructures. Port 315 provides for entry of processes gases, carriergases, and so forth, and port 311 provides for exit of exhaust gases.The susceptor is generally positioned in semi-circular opening 319 sothat its top surface is coplanar with the top of quartz shelf 317.Thereby a substantially smooth surface is presented to process gasesentering from the inlet manifold structures so that these gases can passacross the top of the susceptor without becoming turbulent or beingdiverted under the susceptor. Cylindrical quartz tube 321 provides for asusceptor support shaft on which the susceptor can rotate.Advantageously, carrier gas can be injected through this tube to purgethe volume under the susceptor to prevent dead zones where process gasescan accumulate. In particular, build up of GaCl₃ under the heatedsusceptor is limited.

The inlet manifold structures provide process gases through both port315 and slit-like port 329. Gases reach port 329 first though quartztube 323; this tube opens into flattened funnel 325 which allows gasesto spread transversely (transverse to process gas flow in the reactionchamber); this funnel opens into the base of the reaction chamberthrough a transversely-arranged slot in shelf 317.

With reference to FIG. 6, the funnel is compactly filled with beads ofsilicon carbide 607 and a silicon carbide insert 327 in the top of theflattened funnel provides slit-like port 329 for entry of GaCl₃ fromfunnel 325 into the reaction chamber. Two IR spot lamps 601 and theirreflector optics are located on each side of the funnel. A quartz sheath603 containing a thermocouple 605 is inserted through the bottom of thequartz tube 323 up to about the middle of the funnel height in themiddle of the SiC beads in order to enable close loop control of thespot lamp power to maintain the SiC beads at a temperature of about 800°C. Preferably, GaCl₃ is introduced through port 329 and NH₃ isintroduced through port 315. Alternatively, GaCl₃ can be introducedthrough port 315 and NH₃ can be introduced through port 329.Alternatively, an RF field may be created as known in the art in a lowerportion of tube 323 so that the NH₃ can be activated by the creation ofions or radicals. Alternatively, some or all of the NH₃ can be replacedby N₂ which will be similarly activated by the RF field. A SiC extensionplate 335 is disposed between the slit port 329 and the edge of thesusceptor. This SiC extension plate is heated by the main heating lampsto ensure that the dimer does not reform in the gas phase between theslit-like port 329 and the susceptor. The temperature of the SiCextension plate should be above 700° C. and preferably above 800° C.

FIG. 4 illustrates a diagonally cut-away view of a particular preferredreaction/transfer chamber assembly comprising wafer transfer chamber 401assembly mated to reaction chamber assembly 403. Structures which havebeen previously identified in FIGS. 2 and 3 are identified in thisfigure with the same reference numbers. Exemplary transfer chamber 401houses a robot arm, Bernoulli wand, and other means (not illustrated)for transferring substrates from the outside of the system into thereaction chamber and from the reaction chamber back to the outside.Transfer chambers of other designs can be used in this invention.

The reaction chamber assembly includes reaction chamber 301 mountedwithin shroud 405. Illustrated here are portions of bottom wall 407 andfar wall 205 of the shroud. The shroud serves to conduct cooling airover the reaction chamber to maintain a controlled wall temperature.Certain reaction chamber structures have already been describedincluding: bottom wall 305, side wall 307, flange 309 to outletmanifold, shelf 317, susceptor 215, and cylindrical tube 321 forsusceptor support and optional purge gas flow. The susceptor rotates ina circular opening 319 in rounded plate 409 which provides lateralstability to the susceptor and is coplanar with shelf 317, SiC extensionplate 335 and slit-like port 329. The planarity of these componentsensures a smooth gas flow from the gas inlet to the susceptor. Outletmanifold structures include plenum 407 which conducts exhaust gases fromthe reaction chamber in the indicated directions and into exhaust line419. The outlet manifold and flange 309 on the reaction chamber aresealed together with, e.g., a gasket or O-ring (not illustrated) madefrom temperature and chlorine resistant materials.

Inlet manifold structures (as this term is used herein) are illustratedwithin dashed box 411. Plenum 211, described below, is sealed to thefront flange of the reaction chamber with a gasket or O-ring (notillustrated in FIG. 4, but O-ring 503 in FIG. 5) or the like made fromtemperature and chlorine resistant materials. gate valve 413 between thetransfer chamber and the reaction chamber rotates clockwise (downward)to open a passage between the two chambers, and counterclockwise(upward) to close and seal the passage between the two chambers. Thegate valve can be sealed against face plate 415 by means of, e.g., agasket or O-ring. The preferred material for the O-ring is the same asthat mentioned above for other o-rings. The gate valve preferably alsoprovides ports for gas entry as described below. Preferably, this gatevalve is an embodiment of the above-described gate valve of thisinvention. The structure of the lower gas inlet, as previouslydescribed, includes communicating quartz tube 323, flattened funnel 325,and slit-like port 329.

FIG. 5 illustrates details of the particular preferred inlet manifoldstructures and their arrangement in the reaction chamber assembly.Structures which have been previously identified in FIGS. 2 and 3 areidentified in this figure with the same reference numbers. Consideringfirst the surrounding reaction chamber assembly, reaction chamberassembly 403, including shroud 405 and reaction chamber 301, is at theleft, while transfer chamber structures 401 are at the right. Susceptor215 and susceptor stabilizing plate 409 are inside the reaction chamber.Quartz flange 313 of the reaction chamber is urged against plenumstructure 211 by extension 501 of shroud 405. The reaction chamberflange and plenum structure are sealed by O-ring gasket 503 which isvisible in cross-section on both sides of port 315.

Considering now the inlet structure leading through slit-like port 329for GaCl₃ (preferably, but optionally, NH₃ instead). It is comprised ofa quartz tube 323, and funnel 325 that is longitudinally flattened butextended transversely so that it opens across a significant fraction ofthe bottom wall of the reaction chamber. Small beads or small tubes orany form of a porous IR absorbent material fill the funnel 325. Insert327 fits into the upper opening of the funnel and includes slit-likeport 329 that is angled towards the susceptor with an extension plate335 that covers the space between the susceptor and the slit-like port.In operation, GaCl₃ (and optional carrier gases) moves upward in thesupply tube, spreads transversely in the funnel, and is directed by theslit into the reaction chamber and towards the susceptor. Thereby, GaCl₃moves from port 329 towards susceptor 215 in a laminar flowsubstantially uniform across the width of the reaction chamber.

Considering now inlet structures leading through port 315, thesestructures include plenum structure 211, face plate 415, and gate valve413. NH₃ (preferably, but optionally, GaCl₃ instead) vapor is introducedinto the plenum structure through supply line 517 and passes downwardtowards the reaction chamber through the number of vertical tubes 519.NH₃ vapor then exits the vertical tubes, or optionally throughdistributed ports in which each vertical tube is lined to a group ofdistributed ports, and passes around lip 511 of the plenum. Thereby, NH₃vapor moves towards the susceptor in a laminar flow substantiallyuniform across the width of the reaction chamber. Flow through eachvertical tube is controlled by a separate valve mechanism 509 all ofwhich are externally adjustable 213. The plenum also includes tubes forconducting temperature-control fluids, e.g., GALDEN™ fluid havingtemperatures controlled so that the plenum structures through which NH₃passes are maintained within the above-described temperature ranges andso that plenum structure adjacent to O-ring 503 are maintained withinthe operational range for the sealing materials used in the O-ring. Asnoted, the preferred material for the O-ring is the same as thatmentioned above for other o-rings. Temperature control tube 505 isvisible (a corresponding tube is also visible below port 315) adjacentto O-ring 503. In typically operation, this tube serves to cool theO-ring so that it remains within its operational range.

Gate valve 413 advantageously is an embodiment of the above-describedgate valve of this invention. This gate valve includes a number of gasinlet ports 515 as well as serving to isolate the reaction and transferchambers. It is opened and closed to provide controlled access forwafers and substrates between the transfer chamber and the reactionchamber through port 315. It is illustrated in a closed position inwhich it is sealed to face plate 415 by O-ring 507. In preferredembodiments, gas inlet ports 515 are used to inject purge gases, e.g.,N₂. Their size and spacing, which here is denser near the edge portionsof the gate valve (and reaction chamber) and sparser at the centralportions of the gate valve (and reaction chamber), are designed toimprove the uniformity in composition and velocity of the process gasesas they flow across the susceptor and build a purge gas curtain alongthe side walls of the chamber to prevent GaCl₃ gas from flowingunderneath the susceptor to avoid undesired deposition of GaN in thislocation.

The temperature of the exposed face of gate valve 413 can be raised byproviding heated purge gases. For example, heated N₂ can be circulatedin passageways internal to gate valve 413 and then out through ports 515in the exposed face of this gate valve. The temperature of the sealingportions of gate valve 413 and of reactor member 415 can be lowered bythe cool fluid circulating in passageway 505. Although, this cool fluidprimarily cools O-ring 503 between the reactor and the plenum, byconduction it can secondarily cool O-ring 507 between gate valve 413 andmember 415. Optionally, further cooling of O-ring 507, if necessary, canbe provided by additional passageways for cool fluid in member 415.Preferably, thermocouples (not illustrated) can be placed on and aroundthe gate valve so that the heating and cooling mechanisms can becontrolled.

Generally, for deposition of high quality epitaxial layers the inletmanifold and port structures cooperate to provide a process gas flowthat is substantially laminar (thus non-turbulent) and that issubstantially uniform in velocity and composition. The substantiallylaminar and uniform flow should extend longitudinally up to and over thesusceptor and transversely across the reaction chamber (or at leastacross the surface of the susceptor). Preferably, process gas flows inthe reaction chamber are uniform in velocity and composition across thechamber to at least 5%, or more preferably 2% or 1%. Compositionuniformity means uniformity of the III/V ratio (i.e., GaCl₃/NH₃ ratio).This is achieved by: first, designing the process gas inlet ports toprovide an already approximately uniform flow of process gases throughthe reaction chamber; and second, by designing selective injection ofcarrier gases to cause the approximately uniform flow to becomeincreasingly uniform. Control of flow downstream from the susceptor isless important.

Numerical modeling of the gas flow dynamics of the particular preferredembodiment has determined a preferred process gas inlet portconfiguration so that a substantially uniform flow is produced.Guidelines for total process gas flow rates are established according tothe selected GaN deposition conditions and rates needed for intendedsustained, high-throughput operation. Next, within these overall flowguidelines, insert 327 and slit 329 have been designed so the modeledGaCl₃ flow into the reaction chamber is substantially uniform across thereaction chamber. Also, modeling of intended GaCl₃ flows has indicatedthat after the NH₃ vapor emerges around lip 511 into the reactionchamber, this flow also becomes substantially uniform across thereaction chamber. Further, valves 509 can be controlled to amelioratenon-uniformities that may arise during operation.

Further, guided by numerical modeling, secondary carrier gas inlets havebeen added to increase the uniformity of the primary-process gasesflows. For example, in the particular preferred embodiment, it has beenfound that supply of purge gases through gate valve 413 providesimprovement by preventing accumulation of high concentrations of GaCl₃vapor between the face of gate valve 413 and lip 511 (i.e., the regionsenclosed by face plate 415). Also, it has been found that arranginginlets to provide greater carrier gas flow at the edges of the reactionchamber and lesser purge gas flow at the center also improves uniformityof composition and velocity of flow at the susceptor and bettermaintains the reactive gas above the surface of the susceptor.

Example

The invention is now compared to a standard or conventional HVPE systemto illustrate the advantages and unexpected benefits that are providedwhen conducting HVM of Group III-V material according to the invention.Prior to setting forth this comparison and by way of introduction,conventional HVPE systems are first briefly described in relevant part.

A conventional HVPE system consists of a hot-wall tube furnace usuallyfabricated of quartz. The Group III precursor is formed in-situ in thereactor by flowing HCl over a boat holding the Group III metal in aliquid form. The Group V precursor is supplied from external storage,e.g., a high pressure cylinder. Conventional HVPE has been used for thegrowth of arsenide, phosphide and nitride semiconductors. For the growthof GaN, the Group III source is typically molten Ga in a quartz boat(with which the HCl reacts to form GaCl), and the Group V source isusually ammonia gas.

In more detail, the quartz tube can be oriented either vertically orhorizontally. The surrounding furnace is usually of a resistive typewith at least two temperature zones: one for maintaining the Group IIImetal at a temperature above its melting point; and the other formaintaining the substrate/wafer at a sufficiently high temperature forepitaxial growth. The Group III-metal source equipment including a boatfor liquid Group III metal, the substrate/wafer holder, and gas inletsare placed and arranged in one end of the quartz furnace tube; the otherend serves for exhausting reaction by-products. All this equipment (orat least that which enters the furnace tube) must be fabricated ofquartz; stainless steel cannot be used. Most reactors process only onewafer at a time at atmospheric pressure. Multiple wafers must bearranged in a reactor so that the surfaces of all wafers are directly inline of the gas flow in order to achieve uniform deposition.

Wafers are loaded by first placing them on a substrate support and thenby positioning the substrate support into a high-temperature zone in thequartz furnace tube. Wafers are unloaded by removing the support fromthe furnace and then lifting the wafer off the support. The mechanismfor positioning the substrate support, e.g., a push/pull rod, must alsobe fabricated of quartz since they are also exposed to full growthtemperatures. Supported wafers, the substrate support, and thepositioning mechanism must be positioned in the usually hot reactor tubewith great care in order to prevent thermal damage, e.g., cracking ofthe wafers and/or substrate support. Also, the reactor tube itself canbe exposed to air during wafer loading and unloading.

Such conventional HVPE reactors are not capable of the sustained highvolume manufacturing that is possible with the HVM methods and systemsof this invention for a number of reasons. One reason is that thereactors of this invention require less unproductive heating and coolingtime than do conventional HVPE reactors because they can haveconsiderably lower thermal masses. In the reactors of this invention,only the susceptor (substrate/wafer support) needs to be heated, and itis heated by rapidly-acting IR lamps. Heating and cooling can thus berapid. However, in conventional HVPE reactors, the resistive furnace canrequire prolonged heating and (especially) cooling times, up to severalto tens of hours. During such prolonged heating and cooling times, thissystem is idle, and wafer production, reactor cleaning, systemmaintenance, and the like must be delayed. Furthermore, despite risks ofthermal damage, wafers are usually placed in and removed from thereactor when it is near operating temperatures to avoid further heatingand cooling delays. For these reasons, the systems and methods of thisinvention can achieve higher throughputs than can conventional HVPEsystems.

Another reason limiting the throughput of conventional HVPE systems isthat such systems require considerably more reactor cleaning that do thereactors of this invention. Because all internal components ofconventional HVPE reactors are heated by the external resistive furnace,III-V material can grow throughout the inside of the reactor, and notonly on the substrate where it is desired. Such undesired deposits mustbe frequently cleaned from the reactor or else they can form dust andflakes which contaminates wafers. Cleaning requires time during whichthe reactor is not productive.

Also, the Group III precursor is inefficiently used; most is depositedon the interior of the reactor; a small fraction is deposited on thesubstrate wafer as desired; and little or none appears in the reactorexhaust where it might be recycled for reuse. The Group V precursor isalso inefficiently used, and excess can react with unused HCl to formchlorides (e.g., NH₄Cl) that can deposit on cold areas down stream ofthe reaction zone. Such chloride deposits must also be cleaned from thereactor.

In contrast, the reactors of this invention have temperature controlledwalls so that little or no undesired growth of Group III-V materialoccurs. Reactors of this invention can be more productive sinceunproductive cleaning and maintenance either can be shorter, or need notbe as frequent, or both. For these reasons also, the systems and methodsof this invention can achieve higher throughputs that can conventionalHVPE systems.

Another reason limiting the throughput of conventional HVPE systems isthat their conventional internal Ga sources require recharging (withliquid Ga or other Group III metal) considerably more frequently than dothe external Ga sources of this invention of this invention (which arerecharged with the Ga precursor GaCl₃). The external source of thisinvention delivers a flow of Ga precursor that can be controlled in bothrate and composition at maximum sustained rates up to approximately 200gm/hr or greater. Since the capacity of the external source is notlimited by reactor geometry, it can be sufficient for many days or weeksof sustained production. For example, an external source can store up tomany tens of kilograms of Ga, e.g., approximately 60 kg, and multiplesources can be operated in series for essentially unlimited sustainedproduction.

In conventional HVPE systems, the Ga source has a strictly limitedcapacity. Since the source must fit inside the reactor and can be nolarger than the reactor itself, it is believed that an upper limit to aconventional source is less than 5 kg of Ga. For example, for 3 kg ofGa, a boat of approximately 7×7×20 cm filled with liquid Ga 4 cm deep isrequired. Disclosure of such a large Ga boat has not heretofore beenfound in the prior art. Further the rate and composition of the sourcecannot be well controlled, because the Ga precursor (GaCl) is formed insitu by passing HCl and over the liquid Ga in the Ga source boat insidethe reactor. The efficiency of this reaction is dependent upon reactorgeometry and exact process conditions, e.g., the temperature in thesource zone, and various efficiency values from 60% to over 90% havebeen reported. Furthermore, as the level of the Ga decreases and as theGa source ages, the flux of GaCl to the deposition zone can vary evenwith a constant process conditions. For these reasons also, the systemsand methods of this invention can achieve higher throughputs that canconventional HVPE systems.

Another reason limiting the throughput of conventional HVPE systems isthat heretofore their construction is not standardized, and in fact suchsystems are often individually designed and fabricated for specificusers. Lack of standardization leads to, for example, slow and complexmaintenance. Because they can often include complex and fragile quartzcomponents that are difficult to work with, such reactors aretime-consuming to disassemble and reassemble. In particular, the GroupIII source zone is intricate as it contains a separate quartz inlet forHCl, a quartz boat positioned adjacent to the HCl inlet, a separatequartz inlet for the Group V precursor (which must be kept separate fromthe Group III precursor), and a possible additional quartz inlet for acarrier gas. In contrast, the systems and methods of the presentinvention are to a great extent adaptations of tested and standardizeddesigns known for Si processing, which have been optimized for efficientoperation and maintenance and which include commercially-availablecomponents. For example, the particular preferred embodiment includes aGroup III source zone with a gate valve and Group III precursor plenumand inlet ports partially fabricated from metal. The gate valve requiresonly a short time to open and close, and the Group III precursor plenumand inlet ports are considerably less fragile. For these reasons also,the systems and methods of this invention can achieve higher throughputsthat can conventional HVPE systems.

The qualitative design choices that differentiate systems of thisinvention from conventional HVPE systems leads to surprisingquantitative benefits in epitaxial growth efficiencies, reactorutilizations and wafer production rates, and precursor utilizationefficiencies. These surprising quantitative benefits are reviewed belowusing the data in Tables 1, 2, and 3, which compare a conventional HVPEsystem designed to handle one 100 mm diameter substrate and including areactor tube of about 20 cm in diameter and about 200 cm in length witha corresponding system of this invention.

Considering first achievable epitaxial growth efficiencies, the data ofTable 1 demonstrate that the HVM systems of this invention can beconsiderably more efficient than conventional HVPE systems.

TABLE 1 Epitaxial growth efficiencies Conventional Epitaxial growthefficiencies HVPE HVM Reactor Information Wafer diameter cm 15 15Reactor length cm 200 Reactor diameter cm 20 Hot zone length cm 40 #wafers processed simultaneously 1 1 Reactor production times waferload/unload time Pull/push rate cm/min 2 Total pull and push length cm160 0 Total pull and push time min 80 2 Wafer load/unload time min 9.5 2Total load/unload time min 89.5 3 Operation overhead % 10% 10% Totalload/unload time in cont. min 52.0 2.2 operation epitaxial growth timeTime to grow template min 0 0 Growth rate um/hr 200 (3.3) 200 (3.3)(um/min) Layer thickness um 300 300 Time to heat and cool min 0 6 Timeto grow layer min 90 90 Operation overhead % 10% 10% Total growth timemin 99 106 Total wafer-in-reactor time min 151.0 107.8 Reactorutilization (R.U.) R.U. - growth time/wafer-in- % 66% 98% reactor timeEpitaxial growth efficiencies can be represented by the ratio of theactual epitaxial growth times to the sum of the actual epitaxial growthtimes and the reactor load/unload times. It can be seen that the HVMsystems and methods of this invention can be loaded/unloadedsignificantly faster than can conventional HVPE systems, and thus canachieve higher epitaxial growth efficiencies. It is also expected thatin actual operation, the external Ga sources of this invention willallow sustained operation for considerably longer periods than possiblewith conventional systems.

Because, in conventional HVPE system, the reactor is maintained at neardeposition temperature between runs, the substrate must be pulled fromor pushed into the reactor at a slow enough rate to avoid thermaldamage. Assuming that distance of the substrate holder from the reactorinlet is about 80 cm and a pull rate of no more that 2 cm/min to avoidthermal damage, about 40 min. are required to pull the substrate fromand also to push the substrate into the reactor. Further, once thesubstrate and wafer are positioned in the reactor, up to 10 min can berequired for thermal stabilization, reactor purge, and set-up of processgasses. (With load locks the purge and gas setup might require 5 minuteseach; without load locks, setup would be much longer.) Thus, the totalload/unload time is about 90 min, or 52 min in continuous production(where some times would be shared equally between two successive runs).

In contrast, in the HVM systems of this invention, wafers can be rapidlyloaded/unloaded at lower temperatures without risk of thermal damagethus eliminating extended wafer positioning times. Because of their lowthermal mass and IR-lamp heating, reactors used (and specifically thesusceptor and wafer in such reactors) in the HVM systems and methods ofthis invention can be rapidly cycled between higher depositiontemperatures and lower temperatures loading/unloading temperatures.Therefore, the HVM systems and methods of this invention achieveconsiderably shorter loading/unloading times than are possible inconventional HVPE reactors.

Once loaded and assuming Ga precursor sources used in conventional HVPEsystems are able to maintain an adequate mass flow rate of precursor,actual epitaxial growth times of conventional systems and of the systemsof this invention are of approximately the same magnitude. However, itis expected that the Ga precursor source used in the HVM systems andmethods of this invention has significant advantages over Ga precursorsource used in convention HVPE systems, so that in actual operation thesystems and methods of this invention will achieve relative epitaxialgrowth efficiencies even greater than the efficiencies presented inTable 1.

For example, even if capable of adequate mass flow for an initialperiod, it is unlikely that convention Ga sources can sustain adequatemass flow for extended periods. Conventional HVPE systems generate Gaprecursor in-situ to the reactor by the passing HCl gas over metallicgallium in a liquid form. Because the efficiency of this process dependsstrongly on reactor geometry and process conditions (e.g., from about60% to over about 90% depending on Ga temperature), the actual mass flowof Ga precursor (GaCl) will also vary. Further, as the level of the Gadecreases and the Ga source ages, the flux of Ga precursor can vary evenwith a constant process conditions (e.g., constant temperature and inputHCl flux). Further, conventional Ga sources (in particular the liquid Gaboat) must be within the reactor, and their capacities are thusconstrained by reactor geometry. The largest boat believed to bereasonably possible (and not believed to be disclosed in the known inthe prior art) in a conventional HVPE system could hold no more thanabout approximately 3 to 5 kg and would be approximately 7×7×20 cm insize and be filled 4 cm deep with liquid Ga.

In contrast, the HVM systems and methods of this invention employ anexternal Ga source which can provide constant, unvarying flow of Gaprecursor at up to 200 gm of Ga/hr and greater (sufficient to supportgrowth rates in excess of 300 um/hr) that can be sustained for extendedperiods of time. First, this source can provide GaCl₃ vapor in a mannerso that the Ga mass flux can be measured and controlled even duringepitaxial growth. Second, this external Ga source is capable ofsustained, uninterrupted operation because Ga precursor is supplied froma reservoir holding 10's of kilograms of precursor. Additionally,multiple reservoirs can be operated in series for effectively unlimitedoperation.

In summary, relative epitaxial growth efficiencies can be summarized byreactor utilization (R.U.) defined by the fraction of the time that awafer is in the reactor during which actual growth is occurring. It isseen that the HVM systems and methods of this invention achieve such aR.U. of about 95% or more, while conventional HVPE systems can achievesuch a R.U. of no more than about 65%. And it is expected that the HVMsystems and methods of this invention will achieve even greater relativeepitaxial growth efficiencies in actual operation.

Next considering first achievable reactor utilizations and waferproduction rates, the data of Table 2 demonstrate that the HVM systemsof this invention can be more efficient than conventional HVPE systems.

TABLE 2 Reactor utilizations and achievable wafer production ratesReactor maintenance times and wafer Conventional production rates HVPEHVM in-situ reactor cleaning time # runs between in-situ cleaning 5 5Time to open/close reactor min 26.6 2 Total thickness to be etched um1500 300 Etch rate um/ 8 8 min Etch time min 187.5 18.8 bake time min 3015 Time to load Ga with in-situ etch min 45 0.0 Operation overhead % 18%15% Total in-situ cleaning time min 339.8 41.1 ex-situ reactor cleaningtime # runs between ex-situ cleaning 15 15 time to close reactor afterunloading min 13.3 1.0 time to cool reactor min 180 20 time to takereactor apart min 120 120 time to put reactor back together min 180 120time to leak check and other min 45 45 Time to load Ga with ex-situ etchmin 10 0 time to heat reactor min 75 20 Wafer testing time min 60 60Preventive maintenance min 120 120 Operation overhead % 25% 20% Totalex-situ cleaning time min 959.2 571.2 Reactor utilization (R.U.) andwafer production rate R.U. - wafer-in-reactor time/total use time % 59%76% R.U. - growth time/total use time % 39% 75% # runs (wafers) 15 15total use time for #runs (wafers) min 3734 1996 # wafers/hour 0.24 0.45# hours/wafer 4.15 2.22 # wafers/24 hours 5.8 10.8Reactors must be periodically taken out of production for cleaning andpreventive maintenance. Since the HVM systems and methods of thisinvention can be rapidly cleaned and maintained, they can achieve higherreactor utilizations and wafer production rates than can conventionalHVPE systems.

During operation, materials grow on undesired locations in the reactor,e.g., on the reactor walls and on other internal reactor components, andexcessive growth of these materials can cause problems, e.g., wafercontamination. Cleaning is required to remove these undesired materials,and can be performed either in-situ, that is without disassembling thereactor, or ex-situ, after disassembling the reactor. In-situ cleaningis often performed by etching undesired deposits with HCl. After anumber of in-situ etchings or cleanings, more thorough ex-situ cleaningis advantageous.

HVM systems of this invention require considerably less in-situ cleaningtime than conventional HVPE systems. The reactors of this invention havewalls with controlled lower temperatures so that little materialdeposits thereon during wafer production. In contrast, conventional HVPEreactors operate at higher deposition temperatures so that the sameamount of material grows on reactor walls and internal reactor parts asgrows on the wafers and substrates. Table 2 presents a scenario whichassumes that no more than 1.5 mm of unwanted GaN can be allowed todeposit on reactor walls and internal reactor parts.

For conventional HVPE systems, in-situ cleaning is required every 5runs, during which 1.5 mm of unwanted GaN (300 um per run and) will havegrown on the reactor interior. In contrast, if in-situ cleaning of thereactors of this invention is also performed every 5 runs, only anominal amount (e.g., 20% or less of the amount that will have grown inconventional HVPE systems) of GaN will have grown on the reactorinterior. (In fact, in-situ cleaning of the HVM systems of thisinvention could reasonably be delayed to only every 15 runs.) Therefore,in-situ cleaning times of conventional HVPE reactors are at least 5times (and up to 15 times) longer than the in-situ cleaning time of theHVM reactors of this invention.

Also, the HVM systems of this invention require considerably lessex-situ cleaning time than conventional HVPE systems. First, these HVMsystems have significantly shorter cooling/heating times which mustprecede and follow, respectively, ex-situ cleaning. Also, theirdisassembly/cleaning/reassembly times are similar to the shorter timesknown for Si processing systems, because the HVM systems and methods ofthis invention comprise commercially available designs and componentsalready known for Si processing. The designs and components incorporatedfrom Si processing systems include: rapidly-acting reactor gates, fullyautomated wafer handling with cassette-to-cassette loading, the abilityto perform hot load/unload, separate cooling stages, in-situ growth ratemonitoring and load locks to prevent exposure of the reactor toatmosphere.

And, as already discussed, the Ga precursor sources, i.e., the Ga boat,used in conventional HVPE systems must be periodically recharged inorder both to maintain constant precursor flow and also because of theirlimited capacity. This precursor recharging, which can be performedduring cleaning, further lengthens cleaning times of these conventionalsystems. In contrast, the external Ga sources of the HVM systems andmethods of this invention can operate with little or no interruption forextended periods of time.

In summary, reactor maintenance times can be summarized by a furtherR.U. and a wafer production rate. This second R.U. represents the ratioof the time that a wafer is in the reactor to the sum of the times thata wafer is in the reactor plus the cleaning/maintenance times. It can beseen that the HVM system and methods of this invention achieve a R.U. ofabout 75% or more, while conventional HVPE systems can achieve such aR.U. of no more than about 60%.

Relative system efficiencies can be represented by wafer productionrates, which can be derived by dividing a number of wafers produced bythe total time required to produce these wafers. Since a complete cycleof wafer production runs, in-situ cleanings, and ex-situ cleanings,rates comprises 15 runs (according to the assumptions of Tables 1 and2), these rates are determined by dividing 15 by the total time forproducing 15 wafers (including load/unload time, in-situ cleaning time,in-situ cleaning time, maintenance time, and source recharge time). Itcan be seen that the total time the HVM systems and methods of thisinvention require to produce 15 wafers (runs) is considerably shorterthan the total time required by convention HVPE systems. Therefore, thesystems and methods of this invention achieve an approximately 2 foldthroughput improvement over the prior art. As discussed above, a greaterthroughput improvement is expected during actual operation.

Lastly, considering comparative precursor efficiencies, the HVM systemsand methods of this invention utilize precursors, especially Gaprecursors, more efficiently than conventional HVPE systems. This isexemplified by the data in Table 3.

TABLE 3 Precursor utilizations Conventional Precursor utilization HVPEHVM ammonia (both processes) Ammonia Flow slpm 14 10 Total ammonia flowtime min 132.0 97.7 Total ammonia for 90 min. run mole 82.5 43.6 HCl(convention HVPE) Moles of HCl/min during run mole/min 0.024 Liters HClused in run liter 51.2 gallium (convention HVPE) Input V/III ratio 30Moles/min of ammonia mole/min 0.6250 during run Moles/min of Ga requiredby mole/min 0.0208 ammonia flow Conversion of GaClx to GaN % 95% Actualmoles/min of Ga used mole/min 0.0219 in run Additional moles of Ga % 10%moles of Ga/min for run mole/min 0.024 Weight of Ga/min for run gm/min1.76 gm Ga/min; 100 gm Ga/hr Weight of Ga per run gm 151.4 gallium (HVM)Input V/III ratio 30 moles of ammonia/min mole/min 0.4464 during runmoles/min of Ga to meet V/III mole/min 0.0149 Conversion of GaClx to GaN% 95% moles of GaCl3 dimer/min mole/min 0.0082 required to meet V/IIIAdditional moles of GaCl3 % 10% dimer Total moles GaCl3 dimer for runmole 0.82 Atomic weight GaCl3 dimer gm/mole 352.2 Total weight of GaCl3dimer gm 287.4 for run Percent of GaCl3 dimer that % 40% is Ga Weight ofGa for run gm 114 Weight of Ga/hour for run gm 75 gm Ga/hr Gautilization % 21% 25% Utilization with Ga recycling % 27% 80% (est.)

Ga utilization is determined in Table 3 by, first, considering that aconventional HVPE system suitable for a 15 cm wafer can be expected touse approximately 14 slpm (standard liters per minute) of ammonia.Assuming a V/III ratio of 30 and a 95% conversion of the Ga precursorinto GaN, the conventional system can be expected to use approximately1.8 gm/min of Ga. A 90 minute run sufficient to grow 300 um of GaN at200 um/hr therefore requires about 151 gm of Ga. Since there is about 31gm of Ga in a 300 um layer on a 15 cm wafer, the Ga efficiency of theconventional HVPE reactor is approximately 21% (=31/151). Since most ofthe remaining 120 gm (=151-31) is deposited on the insides of thereactor, little is thus unavailable recycling and reuse. It is expectedthat even with recycling and reuse of Ga exhausted from the reactor, theGa efficiency of the conventional HVPE reactor is no more thanapproximately 25%.

In contrast, HVM systems and methods can be expected to use a lowerammonia flow (e.g., 10 slpm) and therefore a lower Ga flow and a lowertotal Ga required for a 15 cm wafer (e.g., 114 gm). Therefore, the HVMsystems and methods of this invention can achieve Ga efficiencies of 27%(=31/114) without recycling and reuse and up to perhaps 80% or greaterGa efficiency with recycling and reuse of Ga exhausted from the reactor.Additionally, since little of the remaining 83 gm (=114-31) is depositedon the insides of the reactor, most of this unused Ga appears in thereactor exhaust where it is available recycling and reuse. It isexpected that with recycling and reuse of exhaust Ga, the Ga efficiencyof the HVM systems and methods of this invention can reach 80% orgreater.

The preferred embodiments of the invention described above do not limitthe scope of the invention, since these embodiments are illustrations ofseveral preferred aspects of the invention. Any equivalent embodimentsare intended to be within the scope of this invention. Indeed, variousmodifications of the invention in addition to those shown and describedherein, such as alternate useful combinations of the elements described,will become apparent to those skilled in the art from the subsequentdescription. Such modifications are also intended to fall within thescope of the appended claims. In the following (and in the applicationas a whole), headings and legends are used for clarity and convenienceonly.

A number of references are cited herein, the entire disclosures of whichare incorporated herein, in their entirety, by reference for allpurposes. Further, none of the cited references, regardless of howcharacterized above, is admitted as prior art to the invention of thesubject matter claimed herein.

What is claimed is:
 1. A method for forming a monocrystalline GroupIII-V semiconductor material which comprises: reacting an amount of agaseous Group III precursor as one reactant with an amount of a gaseousGroup V component as another reactant in a reaction chamber underconditions sufficient to manufacture the semiconductor material,introducing the reactants so that they react at a predetermined locationin the reaction chamber adjacent and above one or more substrates todeposit semiconductor material thereon, and injecting one or more purgegas streams to assist in directing at least one of the reactants to thepredetermined location.
 2. The method of claim 1 wherein the gaseousGroup III precursor is continuously provided at a mass flow of at least50 g Group III element/hour for a time of at least 48 hours.
 3. Themethod of claim 1 which further comprises injecting the purge gasstreams through a plurality of apertures in a gate valve, the gate valvebeing closable to seal an inlet port of the reaction chamber and beingopenable to allow transfer of materials between the reaction chamberinterior and exterior through the inlet port.
 4. The method of claim 3which further comprises sufficiently controlling the temperature ofportions of the gate valve adjacent to a seal between the gate valvewhen closed and the reaction chamber in order to avoid thermaldeterioration of the seal during operation.
 5. The method of claim 4wherein the gate valve is temperature controlled by passing heatexchange fluids through passages that are conductively-coupled to thegate valve.
 6. The method of claim 3 which further comprisessufficiently heating portions of the gate valve exposed to the reactionchamber interior when closed in order to avoid condensation of and/orunwanted reaction between gases in the reactor.
 7. The method of claim 6wherein the gate valve is heated by passing a heated fluid through oneor more passageways internal to the gate valve.
 8. The method of claim 6wherein the gate valve is sufficiently heated so that the temperature ofthe exposed portions are greater than either or both of a condensationtemperature of the Group III precursor and a sublimation temperature ofa product of a Group III-Group V reaction.
 9. The method of claim 1which further comprises: sealing the reaction chamber with a valve toform a sealed reaction chamber prior to injecting the purge gas therein,wherein the purge gas streams are injected through the valve, and afterthe semiconductor material is deposited upon the one or more substrates,opening the valve for removal of the one or more substrates from thereaction chamber.
 10. The method of claim 9 which further comprisessensing temperatures of the valve and providing feedback for use incontrol of temperature of the valve.
 11. The method of claim 9 whichfurther comprises heating a portion of the valve while the reactionchamber is sealed in order to avoid condensation of and/or unwantedreaction with the reactants.
 12. The method of claim 9 which furthercomprises cooling a portion of the valve while the reaction chamber issealed to maintain sealing of the reaction chamber.
 13. The method ofclaim 12 wherein the cooling is achieved by providing one or morepassages for cooling fluids that are conductively-coupled to the valve.14. The method of claim 1 wherein the reactants enter the reactionchamber as horizontal laminar flows.
 15. The method of claim 1 whereinone of the reactants is introduced into the chamber through a slot thatis configured and dimensioned to direct the reactant to thepredetermined location for reaction with another reactant.
 16. Themethod of claim 1 wherein the Group III precursor is introduced into thereaction chamber to provide the Group III element at a deposition rateof at least 50 g/hour.